Altered gene expression of histone deacetylases in mood disorder patients

Hippocampal HDAC5-mediated histone acetylation underlies stress susceptibility in mice exposed to chronic social defeat stress

Chronic stress leads to social avoidance and anhedonia in susceptible individuals, a phenomenon that has been observed in both human and animal models. Nevertheless, the underlying molecular mechanisms underpinning stress susceptibility and resilience remain largely unclear. There is growing evidence that epigenetic histone deacetylase (HDAC) mediated histone acetylation is involved in the modulation of depressive-related behaviors. We hypothesized that histone deacetylase 5 (HDAC5), which is associated with stress-related behaviors and antidepressant response, may play a vital role in the susceptibility to chronic stress. In the current study, we detected the levels of HDAC5 and acetylation of histone 4 (H4) in the hippocampus subsequent to chronic social defeat stress (CSDS) in C57BL/6J mice. We found that CSDS induces a notable increase in HDAC5 expression, concomitant with a reduction in the acetylation of histone H4 at lysine 12 (H4K12) in the hippocampus of susceptible mice. Meanwhile, intrahippocampal infusion of HDAC5 shRNA or HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) both reversed the depression susceptibility in susceptible mice that subjected to CSDS. Furthermore, HDAC5 overexpression was sufficient to induce depression susceptibility following microdefeat stress, accompanied by a significant reduction in H4K12 level within the hippocampus of mice. Additionally, the Morris water maze (MWM) results indicated that neither CSDS nor HDAC5 exerted significant effects on spatial memory function in mice. Taken together, these investigations indicated that HDAC5-modulated histone acetylation is implicated in regulating the depression susceptibility, and may be serve as potential preventive targets for susceptible individuals.

Microglial forkhead box O3a deficiency attenuates LPS-induced neuro-inflammation and depressive-like behaviour through regulating the expression of peroxisome proliferator-activated receptor-γ

BACKGROUND AND PURPOSE

Depression is closely linked with microglial activation and neuro-inflammation. Peroxisome proliferator-activated receptor-γ (PPAR-γ) plays an important role in M2 activation of microglia. Forkhead box (FOX) O3a has been implicated in the regulation of mood-relevant behaviour. However, little is known about the inflammatory mechanisms of in the microglia of the brain. Here, we have investigated the role of microglial FOXO3a/PPAR-γ in the development of depression.

EXPERIMENTAL APPROACH

The effect of FOXO3a on microglia inflammation was analysed in vitro and in lipopolysaccharide (LPS)-induced depression-like behaviours in vivo. ChIP-seq and Dual-luciferase reporter assays were used to confirm the interaction between FOXO3a and PPAR-γ. Behavioural changes were measured, while inflammatory cytokines, microglial phenotype and morphological properties were determined by ELISA, qRT-PCR, western blotting and immunostaining.

KEY RESULTS

Overexpression of FOXO3a significantly attenuated expression of PPAR-γ and enhanced the microglial polarization towards the M1 phenotype, while knockdown of FOXO3a had the opposite effect. FOXO3a binds to the promoters of PPAR-γ and decreases its transcription activity. Importantly, deacetylation and activation of FOXO3a regulate LPS-induced neuro-inflammation by inhibiting the expression of PPAR-γ in microglia cells, supporting the antidepressant potential of histone deacetylase inhibitors. Microglial FOXO3a deficiency in mice alleviated LPS-induced neuro-inflammation and depression-like behaviours but failed to reduce anxiety behaviour, whereas pharmacological inhibition of PPAR-γ by GW9662 restored LPS-induced microglial activation and depressive-like behaviours in microglial FOXO3a-deficient mice.

CONCLUSION AND IMPLICATIONS

FOXO3a/PPAR-γ axis plays an important role in microglial activation and depression, identifying a new therapeutic avenue for the treatment of major depression.

Trichostatin A relieves anxiety-and depression-like symptoms in APP/PS1 mice

Background

Cognitive deficits and behavioral disorders such as anxiety and depression are common manifestations of Alzheimer's disease (AD). Our previous work demonstrated that Trichostatin A (TSA) could alleviate neuroinflammatory plaques and improve cognitive disorders. AD, anxiety, and depression are all associated with microglial inflammation. However, whether TSA could attenuate anxiety- and depression-like behaviors in APP/PS1 mice through anti-inflammatory signaling is still unclearly.

Methods

In the present study, all mice were subjected to the open field, elevated plus maze, and forced swim tests to assess anxiety- and depression-related behaviors after TSA administration. To understand the possible mechanisms underlying the behavioral effects observed, CST7 was measured in the hippocampus of mice and LPS-treated BV2 microglia.

Results

The results of this study indicated that TSA administration relieved the behaviors of depression and anxiety in APP/PS1 mice, and decreased CST7 levels in the hippocampus of APP/PS1 mice and LPS-induced BV2 cells.

Conclusion

Overall, these findings support the idea that TSA might be beneficial for reducing neurobehavioral disorders in AD and this could be due to suppression of CST7-related microglial inflammation.

Antidepressant effect of the novel histone deacetylase-5 inhibitor T2943 in a chronic restraint stress mouse model

Depression is a prevalent and debilitating psychiatric illness. However, the antidepressant drugs currently prescribed are only effective in a limited group of patients. Histone modifications mediated by histone acetylation are considered to play an important role in the pathogenesis and treatment of depression. Recent studies have revealed that histone deacetylase inhibitors may be involved in the pathogenesis of depression and the underlying mechanism of the antidepressant therapeutic action. Here, we first conducted virtual screening of histone deacetylase-5 (HDAC5) inhibitors against HDAC5, a target closely related to depression, and identified compound T2943, further verifying its inhibitory effect on enzyme activities in vitro. After stereotaxic injection of T2943 into the hippocampus of mice, the antidepressant effect of T2943 was evaluated using behavioral experiments. We also used different proteomic and molecular biology analyses to determine and confirm that T2943 promoted histone 3 lysine 14 acetylation (H3K14ac) by inhibiting HDAC5 activity. Following the overexpression of adenoviral HDAC5 in the hippocampus of mice and subsequent behavioral analyses, we confirmed that T2943 exerts antidepressant effects by inhibiting HDAC5 activity. Our findings highlight the efficacy of targeting HDAC5 to treat depression and demonstrate the potential of using T2943 as an antidepressant.

Evolution of Slow-Binding Inhibitors Targeting Histone Deacetylase Isoforms

Because the overexpression of histone deacetylase enzymes (HDACs) has been linked to numerous diseases, including various cancers and neurodegenerative disorders, HDAC inhibitors have emerged as promising therapeutic agents. However, most HDAC inhibitors lack both subclass and isoform selectivity, which leads to potential toxicity. Unlike classical hydroxamate HDAC inhibitors, slow-binding HDAC inhibitors form tight and prolonged bonds with HDAC enzymes. This distinct mechanism of action improves both selectivity and toxicity profiles, which makes slow-binding HDAC inhibitors a promising class of therapeutic agents for various diseases. Therefore, the development of slow-binding HDAC inhibitors that can effectively target a wide range of HDAC isoforms is crucial. This Perspective provides valuable insights into the potential and progress of slow-binding HDAC inhibitors as promising drug candidates for the treatment of various diseases.

Crotonylation and disease: Current progress and future perspectives

Histone lysine crotonylation was first identified as a new type of post-translational modification in 2011. In recent years, prominent progress has been made in the study of histone and nonhistone crotonylation in reproduction, development, and disease. Although the regulatory enzyme systems and targets of crotonylation partially overlap with those of acetylation, the peculiar CC bond structure of crotonylation suggests that crotonylation may have specific biological functions. In this review, we summarize the latest research progress regarding crotonylation, especially its regulatory factors and relationship with diseases, which suggest further research directions for crotonylation and provide new ideas for developing disease intervention and treatment regimens.

Epigenetic regulation in major depression and other stress-related disorders: molecular mechanisms, clinical relevance and therapeutic potential

Major depressive disorder (MDD) is a chronic, generally episodic and debilitating disease that affects an estimated 300 million people worldwide, but its pathogenesis is poorly understood. The heritability estimate of MDD is 30-40%, suggesting that genetics alone do not account for most of the risk of major depression. Another factor known to associate with MDD involves environmental stressors such as childhood adversity and recent life stress. Recent studies have emerged to show that the biological impact of environmental factors in MDD and other stress-related disorders is mediated by a variety of epigenetic modifications. These epigenetic modification alterations contribute to abnormal neuroendocrine responses, neuroplasticity impairment, neurotransmission and neuroglia dysfunction, which are involved in the pathophysiology of MDD. Furthermore, epigenetic marks have been associated with the diagnosis and treatment of MDD. The evaluation of epigenetic modifications holds promise for further understanding of the heterogeneous etiology and complex phenotypes of MDD, and may identify new therapeutic targets. Here, we review preclinical and clinical epigenetic findings, including DNA methylation, histone modification, noncoding RNA, RNA modification, and chromatin remodeling factor in MDD. In addition, we elaborate on the contribution of these epigenetic mechanisms to the pathological trait variability in depression and discuss how such mechanisms can be exploited for therapeutic purposes.

Research on Xiaoyao Powder in the treatment of depression based on epigenetics and quality markers

Depression has become one of the most common public health issues around the world, and the incidence has been increasing in recent years. A large amount of clinical investigations have proven that the treatment of depression is difficult. The prognosis is poor, and the fatality rate is high. At present, western medicine is the preferred treatment for depression, but it often causes adverse clinical reactions such as dry mouth, blurred vision, and memory loss, etc. The herbal compound Xiaoyao Powder is a traditional medicine for soothing the liver and relieving depression, strengthening the spleen, and nourishing the blood. It can reduce adverse reactions. It is effective in treating depression. In this study, we elucidate the function of Xiaoyao Powder in anti-depression from the perspective of clinical application and pharmacological mechanisms such as regulating epigenetic and chemical quality markers to provide empirical and experimental theoretical results that contribute to developing future depression therapy with Xiaoyao Powder.

Individual differences in social homeostasis

The concept of “social homeostasis”, introduced by Matthews and Tye in 2019, has provided a framework with which to consider our changing individual needs for social interaction, and the neurobiology underlying this system. This model was conceived as including detector systems, a control center with a setpoint, and effectors which allow us to seek out or avoid additional social contact. In this article, we review and theorize about the many different factors that might contribute to the setpoint of a person or animal, including individual, social, cultural, and other environmental factors. We conclude with a consideration of the empirical challenges of this exciting new model.

Genomics in Treatment Development

The Human Genome Project mapped the 3 billion base pairs in the human genome, which ushered in a new generation of genomically focused treatment development. While this has been very successful in other areas, neuroscience has been largely devoid of such developments. This is in large part because there are very few neurological or mental health conditions that are related to single-gene variants. While developments in pharmacogenomics have been somewhat successful, the use of genetic information in practice has to do with drug metabolism and adverse reactions. Studies of drug metabolism related to genetic variations are an important part of drug development. However, outside of cancer biology, the actual translation of genomic information into novel therapies has been limited. Epigenetics, which relates in part to the effects of the environment on DNA, is a promising newer area of relevance to CNS disorders. The environment can induce chemical modifications of DNA (e.g., cytosine methylation), which can be induced by the environment and may represent either shorter- or longer-term changes. Given the importance of environmental influences on CNS disorders, epigenetics may identify important treatment targets in the future.

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

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

Epigenetics in depression and gut-brain axis: A molecular crosstalk

Gut-brain axis is a dynamic, complex, and bidirectional communication network between the gut and brain. Changes in the microbiota-gut-brain axis are responsible for developing various metabolic, neurodegenerative, and neuropsychiatric disorders. According to clinical and preclinical findings, the gut microbiota is a significant regulator of the gut-brain axis. In addition to interacting with intestinal cells and the enteric nervous system, it has been discovered that microbes in the gut can modify the central nervous system through metabolic and neuroendocrine pathways. The metabolites of the gut microbiome can modulate a number of diseases by inducing epigenetic alteration through DNA methylation, histone modification, and non-coding RNA-associated gene silencing. Short-chain fatty acids, especially butyrate, are well-known histone deacetylases inhibitors. Similarly, other microbial metabolites such as folate, choline, and trimethylamine-N-oxide also regulate epigenetics mechanisms. Furthermore, various studies have revealed the potential role of microbiome dysbiosis and epigenetics in the pathophysiology of depression. Hence, in this review, we have highlighted the role of gut dysbiosis in epigenetic regulation, causal interaction between host epigenetic modification and the gut microbiome in depression and suggest microbiome and epigenome as a possible target for diagnosis, prevention, and treatment of depression.

Kinase signalling in excitatory neurons regulates sleep quantity and depth

Progress has been made in the elucidation of sleep and wakefulness regulation at the neurocircuit level^1,2. However, the intracellular signalling pathways that regulate sleep and the neuron groups in which these intracellular mechanisms work remain largely unknown. Here, using a forward genetics approach in mice, we identify histone deacetylase 4 (HDAC4) as a sleep-regulating molecule. Haploinsufficiency of Hdac4, a substrate of salt-inducible kinase 3 (SIK3)³, increased sleep. By contrast, mice that lacked SIK3 or its upstream kinase LKB1 in neurons or with a Hdac4^S245A mutation that confers resistance to phosphorylation by SIK3 showed decreased sleep. These findings indicate that LKB1-SIK3-HDAC4 constitute a signalling cascade that regulates sleep and wakefulness. We also performed targeted manipulation of SIK3 and HDAC4 in specific neurons and brain regions. This showed that SIK3 signalling in excitatory neurons located in the cerebral cortex and the hypothalamus positively regulates EEG delta power during non-rapid eye movement sleep (NREMS) and NREMS amount, respectively. A subset of transcripts biased towards synaptic functions was commonly regulated in cortical glutamatergic neurons through the expression of a gain-of-function allele of Sik3 and through sleep deprivation. These findings suggest that NREMS quantity and depth are regulated by distinct groups of excitatory neurons through common intracellular signals. This study provides a basis for linking intracellular events and circuit-level mechanisms that control NREMS.

Effects of Histone Modification in Major Depressive Disorder

Major depressive disorder (MDD) is a disease associated with many factors; specifically, environmental, genetic, psychological, and biological factors play critical roles. Recent studies have demonstrated that histone modification may occur in the human brain in response to severely stressful events, resulting in transcriptional changes and the development of MDD. In this review, we discuss five different histone modifications, histone methylation, histone acetylation, histone phosphorylation, histone crotonylation and histone β-hydroxybutyrylation, and their relationships with MDD. The utility of histone deacetylase (HDAC) inhibitors (HDACis) for MDD treatment is also discussed. As a large number of MDD patients in China have been treated with traditional Chineses medicine (TCM), we also discuss some TCM therapies, such as Xiaoyaosan (XYS), and their effects on histone modification. In summary, targeting histone modification may be a new strategy for elucidating the mechanism of MDD and a new direction for MDD treatment.

Challenges in Analyzing Functional Epigenetic Data in Perspective of Adolescent Psychiatric Health

The formative period of adolescence plays a crucial role in the development of skills and abilities for adulthood. Adolescents who are affected by mental health conditions are at risk of suicide and social and academic impairments. Gene–environment complementary contributions to the molecular mechanisms involved in psychiatric disorders have emphasized the need to analyze epigenetic marks such as DNA methylation (DNAm) and non-coding RNAs. However, the large and diverse bioinformatic and statistical methods, referring to the confounders of the statistical models, application of multiple-testing adjustment methods, questions regarding the correlation of DNAm across tissues, and sex-dependent differences in results, have raised challenges regarding the interpretation of the results. Based on the example of generalized anxiety disorder (GAD) and depressive disorder (MDD), we shed light on the current knowledge and usage of methodological tools in analyzing epigenetics. Statistical robustness is an essential prerequisite for a better understanding and interpretation of epigenetic modifications and helps to find novel targets for personalized therapeutics in psychiatric diseases.

Corticosterone-mediated regulation and functions of miR-218-5p in rat brain

Chronic stress is one of the key precipitating factors in major depressive disorder (MDD). Stress associated studies have underscored the mechanistic role of epigenetic master players like microRNAs (miRNAs) in depression pathophysiology at both preclinical and clinical levels. Previously, we had reported changes in miR-218-5p expression in response to corticosterone (CORT) induced chronic stress. MiR-218-5p was one of the most significantly induced miRNAs in the prefrontal cortex (PFC) of rats under chronic stress. In the present report, we have investigated how chronic CORT exposure mechanistically affected miR-218-5p expression in the rat brain and how miR-218 could trigger molecular changes on its downstream regulatory pathways. Elevated expression of miR-218-5p was found in the PFC of CORT-treated rats. A glucocorticoid receptor (GR) targeted Chromatin-Immunoprecipitation (ChIP) assay revealed high GR occupancy on the promoter region of Slit3 gene hosting miR-218-2 in its 3rd intron. RNA-sequencing data based on RNA Induced silencing Complex Immunoprecipitation (RISC-IP) with AGO2 in SH-SY5Y cells detected six consistent target genes of miR-218-5p (APOL4, DTWD1, BNIP1, METTL22, SNAPC1, and HDAC6). The expression of all five genes, except APOL4, was successfully validated with qPCR in CORT-treated rat PFC. Further, Hdac6-based ChIP-seq experiment helped in mapping major genomic loci enriched for intergenic regions in the PFC of CORT-treated rat. A proximity-based gene ontology (GO) analysis revealed a majority of the intergenic sites to be part of key genes implicated in central nervous system functions, notably synapse organization, neuron projection morphogenesis, and axonogenesis. Our results suggest that the upregulation of miR-218-5p in PFC of CORT-treated rats possibly resulted from GR biding in the promoter region of Slit3 gene. Interestingly, Hdac6 was one of the consistent target genes potentially found to regulate CNS related genes by chromatin modification. Collectively, these findings establish the role of miR-218-5p in chronic stress and the epigenetic function it plays to induce chromatin-based transcriptional changes of several CNS genes in triggering stress-induced disorders, including depression. This also opens up the scope to understand the role of miR-218-5p as a potential target for noncoding RNA therapeutics in clinical depression.

The Mechanisms Behind Rapid Antidepressant Effects of Ketamine: A Systematic Review With a Focus on Molecular Neuroplasticity

The mechanism of action underlying ketamine's rapid antidepressant effects in patients with depression, both suffering from major depressive disorder (MDD) and bipolar disorder (BD), including treatment resistant depression (TRD), remains unclear. Of the many speculated routes that ketamine may act through, restoring deficits in neuroplasticity may be the most parsimonious mechanism in both human patients and preclinical models of depression. Here, we conducted a literature search using PubMed for any reports of ketamine inducing neuroplasticity relevant to depression, to identify cellular and molecular events, relevant to neuroplasticity, immediately observed with rapid mood improvements in humans or antidepressant-like effects in animals. After screening reports using our inclusion/exclusion criteria, 139 publications with data from cell cultures, animal models, and patients with BD or MDD were included (registered on PROSPERO, ID: CRD42019123346). We found accumulating evidence to support that ketamine induces an increase in molecules involved in modulating neuroplasticity, and that these changes are paired with rapid antidepressant effects. Molecules or complexes of high interest include glutamate, AMPA receptors (AMPAR), mTOR, BDNF/TrkB, VGF, eEF2K, p70S6K, GSK-3, IGF2, Erk, and microRNAs. In summary, these studies suggest a robust relationship between improvements in mood, and ketamine-induced increases in molecular neuroplasticity, particularly regarding intracellular signaling molecules.

Epigenetic mechanisms impacted by chronic stress across the rodent lifespan

Exposures to stress at all stages of development can lead to long-term behavioural effects, in part through changes in the epigenome. This review describes rodent research suggesting that stress in prenatal, postnatal, adolescent and adult stages leads to long-term changes in epigenetic regulation in the brain which have causal impacts on rodent behaviour. We focus on stress-induced epigenetic changes that have been linked to behavioural deficits including poor learning and memory, and increased anxiety-like and depressive-like behaviours. Interestingly, aspects of these stress-induced behavioural changes can be transmitted to offspring across several generations, a phenomenon that has been proposed to result via epigenetic mechanisms in the germline. Here, we also discuss evidence for the differential impact of stress on the epigenome in males and females, conscious of the fact that the majority of published studies have only investigated males. This has led to a limited picture of the epigenetic impact of stress, highlighting the need for future studies to investigate females as well as males.

Antidepressant-like Effects of Combined Fluoxetine and Zinc Treatment in Mice Exposed to Chronic Restraint Stress Are Related to Modulation of Histone Deacetylase

Chronic stress is the key factor contributing to the development of depressive symptoms. Chronic restraint stress (CRS) is well validated and is one of the most commonly used models to induce depressive-like behavior in rodents. The present study aimed to evaluate whether fluoxetine (FLU 5 mg/kg) and zinc (Zn 10mg/kg) given simultaneously induce a more pronounced antidepressant-like effect in the CRS model than both those compounds given alone. Behavioral assessment was performed using the tail suspension and splash tests (TST and ST, respectively). Furthermore, the effects of CRS, FLU and Zn given alone and combined treatment with FLU + Zn on the expression of proteins involved in the apoptotic, inflammatory, and epigenetic processes were evaluated in selected brain structures (prefrontal cortex, PFC; and hippocampus, Hp) using Western blot analysis or enzyme-linked immunosorbent assays (ELISA). The results obtained indicated that three hours (per day) of immobilization for 4 weeks induced prominent depressive symptoms that manifested as increased immobility time in the TST, as well as decreased number and grooming time in the ST. Behavioral changes induced by CRS were reversed by both FLU (5 and 10 mg/kg) or Zn (10 mg/kg). Zinc supplementation (10 mg/kg) slightly increases the effectiveness of FLU (5 mg/kg) in the TST. However, it significantly increased the activity of FLU in the ST compared to the effect induced by FLU and Zn alone. Biochemical studies revealed that neither CRS nor FLU and Zn given alone or in combined treatment alter the expression of proteins involved in apoptotic or inflammatory processes. CRS induced major alterations in histone deacetylase (HDAC) levels by increasing the level of HADC1 and decreasing the level of HADC4 in the PFC and Hp, decreasing the level of HADC6 in the PFC but increasing it in Hp. Interestingly, FLU + Zn treatment reversed CRS-induced changes in HDAC levels in the Hp, indicating that HDAC modulation is linked to FLU + Zn treatment and this effect is structure-specific.

A Multiscale View of the Mechanisms Underlying Ketamine's Antidepressant Effects: An Update on Neuronal Calcium Signaling

Major depressive disorder (MDD) is a debilitating disease characterized by depressed mood, loss of interest or pleasure, suicidal ideation, and reduced motivation or hopelessness. Despite considerable research, mechanisms underlying MDD remain poorly understood, and current advances in treatment are far from satisfactory. The antidepressant effect of ketamine is among the most important discoveries in psychiatric research over the last half-century. Neurobiological insights into the ketamine’s effects have shed light on the mechanisms underlying antidepressant efficacy. However, mechanisms underlying the rapid and sustained antidepressant effects of ketamine remain controversial. Elucidating such mechanisms is key to identifying new therapeutic targets and developing therapeutic strategies. Accumulating evidence demonstrates the contribution of the glutamatergic pathway, the major excitatory neurotransmitter system in the central nervous system, in MDD pathophysiology and antidepressant effects. The hypothesis of a connection among the calcium signaling cascade stimulated by the glutamatergic system, neural plasticity, and epigenetic regulation of gene transcription is further supported by its associations with ketamine’s antidepressant effects. This review briefly summarizes the potential mechanisms of ketamine’s effects with a specific focus on glutamatergic signaling from a multiscale perspective, including behavioral, cellular, molecular, and epigenetic aspects, to provide a valuable overview of ketamine’s antidepressant effects.

The Function and related Diseases of Protein Crotonylation

Crotonylation is a kind of newly discovered acylation modification. Thousands of crotonylation sites have been identified in histone and non-histone proteins over the past decade. As a modification closely related to acetylation, crotonylation was reported to share many universal enzymes with acetylation. Crotonylated proteins have important roles in the regulation of various biological processes, such as gene expression, process of spermatogenesis, cell cycle, and also in the pathogenesis of different diseases, which range from depression to cancer. In this review, we summarize the research processes of crotonylation and discuss the advances of regulation mechanism of both histone and non-histone proteins crotonylation in difference physiological processes. Also, we focus on the alteration of the crotonylation under certain pathological conditions and its role in the pathogenesis of each disease.

Exploring the Role of Nutraceuticals in Major Depressive Disorder (MDD): Rationale, State of the Art and Future Prospects

Major depressive disorder (MDD) is a complex and common disorder, with many factors involved in its onset and development. The clinical management of this condition is frequently based on the use of some pharmacological antidepressant agents, together with psychotherapy and other alternatives in most severe cases. However, an important percentage of depressed patients fail to respond to the use of conventional therapies. This has created the urgency of finding novel approaches to help in the clinical management of those individuals. Nutraceuticals are natural compounds contained in food with proven benefits either in health promotion or disease prevention and therapy. A growing interest and economical sources are being placed in the development and understanding of multiple nutraceutical products. Here, we summarize some of the most relevant nutraceutical agents evaluated in preclinical and clinical models of depression. In addition, we will also explore less frequent but interest nutraceutical products which are starting to be tested, also evaluating future roads to cover in order to maximize the benefits of nutraceuticals in MDD.

Involvement of 5-HT1A receptor-mediated histone acetylation in the regulation of depression

Depression is one of the most common and disabling mental disorders. There is growing evidence that 5-HT1A receptor is involved in the regulation of depressive-related behaviors. However, the exact mechanism underlying the role of 5-HT1A receptor in depression remains unknown. Histone acetylation is associated with the pathophysiology and treatment of depression. In the current study, we investigated whether the epigenetic histone deacetylase (HDAC)-induced histone acetylation mediates the regulation of 5-HT1A receptor in depressive behaviors. We showed that 5-HT1A receptor selective agonist (±)-8-hydroxy-2-(dipropylamino) tetralin hydrobromide led to significant increase in acetylation of H3 at lysine 9 (Ac-H3K9) and H4 at lysine 5 (Ac-H4K5) and lysine 12 (Ac-H4K12) with obviously decreasing histone deacetylase 1 (HDAC1), histone deacetylase 2 (HDAC2), histone deacetylase 4 (HDAC4) and histone deacetylase 5 (HDAC5) expression in hippocampus of mice. Conversely, 5-HT1A receptor selective antagonist NAN-190 decreased the level of acetylation of H3 and H4 with increasing the expression of HDAC1, HDAC2, HDAC4 and HDAC5 in the hippocampus. Furthermore, we found that HDAC inhibitors, trichostatin A or suberoylanilide hydroxamic acid infusion to hippocampus prevented the depressive behaviors induced by NAN-190, as well as histone H3 and H4 acetylation in mice. Our results suggested that epigenetic histone acetylation coupled with 5-HT1A receptor may play vital role in the pathophysiology and treatment of depressive disorders.

The Molecular Basis of Depression: Implications of Sex-Related Differences in Epigenetic Regulation

Major depressive disorder (MDD) is a leading cause of disability worldwide. Although the etiology and pathophysiology of MDD remain poorly understood, aberrant neuroplasticity mediated by the epigenetic dysregulation of gene expression within the brain, which may occur due to genetic and environmental factors, may increase the risk of this disorder. Evidence has also been reported for sex-related differences in the pathophysiology of MDD, with female patients showing a greater severity of symptoms, higher degree of functional impairment, and more atypical depressive symptoms. Males and females also differ in their responsiveness to antidepressants. These clinical findings suggest that sex-dependent molecular and neural mechanisms may underlie the development of depression and the actions of antidepressant medications. This review discusses recent advances regarding the role of epigenetics in stress and depression. The first section presents a brief introduction of the basic mechanisms of epigenetic regulation, including histone modifications, DNA methylation, and non-coding RNAs. The second section reviews their contributions to neural plasticity, the risk of depression, and resilience against depression, with a particular focus on epigenetic modulators that have causal relationships with stress and depression in both clinical and animal studies. The third section highlights studies exploring sex-dependent epigenetic alterations associated with susceptibility to stress and depression. Finally, we discuss future directions to understand the etiology and pathophysiology of MDD, which would contribute to optimized and personalized therapy.

Epigenetic histone acetylation and Bdnf dysregulation in the hippocampus of rats exposed to repeated, low-dose diisopropylfluorophosphate

AIMS

Deployment-related exposures to organophosphate (OP) compounds are implicated for Gulf War Illness (GWI) development in First GW veterans. However, reasons for the persistence of GWI are not fully understood. Epigenetic modifications to chromatin are regulatory mechanisms that can adaptively or maladaptively respond to external stimuli. These include DNA methylation and histone acetylation. DNA methylation changes have been reported in GWI but the role of histone acetylation in GWI has been less explored, despite its importance as an epigenetic mechanism for neurological disorders.

MAIN METHODS

Male Sprague-Dawley rats were exposed to OP diisopropyl fluorophosphate (DFP, 0.5 mg/kg s.c., 5-d) and 6-m later brains were dissected for hippocampus. Western blotting, activity assays and chromatin immunoprecipitation (ChIP) were utilized for epigenetic analyses. Behavior was assessed using the Forced Swim Test (FST) and the Elevated Plus Maze (EPM).

KEY FINDINGS

We observed a significant upregulation in HDAC1 protein along with a significant increase in HDAC enzyme activity in the hippocampus of DFP rats. A locus-specific ChIP study revealed decreases in H3K9ac at the brain derived neurotrophic factor (Bdnf) promoter IV coupled with a significant decrease in BDNF protein in DFP rat hippocampus. Treatment with HDAC inhibitor valproic acid reduced HDAC activity and decreased the FST immobility time in DFP rats.

SIGNIFICANCE

Our research suggests that epigenetic alterations to histone acetylation pathways and decreased BDNF expression could represent novel mechanisms for GWI symptomatology and may provide new targets for developing effective drugs for GWI treatment.

Apocynin Prevents Anxiety-Like Behavior and Histone Deacetylases Overexpression Induced by Sub-Chronic Stress in Mice

Anxiety disorders are common mental health diseases affecting up to 7% of people around the world. Stress is considered one of the major environmental risk factors to promote anxiety disorders through mechanisms involving epigenetic changes. Moreover, alteration in redox balance and increased reactive oxygen species (ROS) production have been detected in anxiety patients and in stressed-animal models of anxiety. Here we tested if the administration of apocynin, a natural origin antioxidant, may prevent the anxiety-like phenotype and reduction of histone acetylation induced by a subchronic forced swimming stress (FSS) paradigm. We found that apocynin prevented the enhanced latency time in the novelty-suppressed feeding test, and the production of malondialdehyde induced by FSS. Moreover, apocynin was able to block the upregulation of p47phox, a key subunit of the NADPH oxidase complex. Finally, apocynin prevented the rise of hippocampal Hdac1, Hdac4 and Hdac5, and the reduction of histone-3 acetylation levels promoted by FSS exposure. In conclusion, our results provide evidence that apocynin reduces the deleterious effect of stress and suggests that oxidative stress may regulate epigenetic mechanisms.

Epigenetic Targeting of Histone Deacetylases in Diagnostics and Treatment of Depression

Depression is a highly prevalent, disabling, and often chronic illness that places substantial burdens on patients, families, healthcare systems, and the economy. A substantial minority of patients are unresponsive to current therapies, so there is an urgent need to develop more broadly effective, accessible, and tolerable therapies. Pharmacological regulation of histone acetylation level has been investigated as one potential clinical strategy. Histone acetylation status is considered a potential diagnostic biomarker for depression, while inhibitors of histone deacetylases (HDACs) have garnered interest as novel therapeutics. This review describes recent advances in our knowledge of histone acetylation status in depression and the therapeutic potential of HDAC inhibitors.

The "missing heritability"-Problem in psychiatry: Is the interaction of genetics, epigenetics and transposable elements a potential solution?

Psychiatric disorders exhibit an enormous burden on the health care systems worldwide accounting for around one-third of years lost due to disability among adults. Their etiology is largely unknown and diagnostic classification is based on symptomatology and course of illness and not on objective biomarkers. Most psychiatric disorders are moderately to highly heritable. However, it is still unknown what mechanisms may explain the discrepancy between heritability estimates and the present data from genetic analysis. In addition to genetic differences also epigenetic modifications are considered as potentially relevant in the transfer of susceptibility to psychiatric diseases. Though, whether or not epigenetic alterations can be inherited for many generations is highly controversial. In the present article, we will critically summarize both the genetic findings and the results from epigenetic analyses, including also those of noncoding RNAs. We will argue that one possible solution to the "missing heritability" problem in psychiatry is a potential role of retrotransposons, the exploration of which is presently only in its beginnings.

The Importance of Epigenetics in Diagnostics and Treatment of Major Depressive Disorder

Recent studies imply that there is a tight association between epigenetics and a molecular mechanism of major depressive disorder (MDD). Epigenetic modifications, i.e., DNA methylation, post-translational histone modification and interference of microRNA (miRNA) or long non-coding RNA (lncRNA), are able to influence the severity of the disease and the outcome of the therapy. This article summarizes the most recent literature data on this topic, i.e., usage of histone deacetylases as therapeutic agents with an antidepressant effect and miRNAs or lncRNAs as markers of depression. Due to the noteworthy potential of the role of epigenetics in MDD diagnostics and therapy, we have gathered the most relevant data in this area.

Acetate supplementation produces antidepressant-like effect via enhanced histone acetylation

BACKGROUND

Abnormal energy metabolism is often documented in the brain of patients and rodents with depression. In metabolic stress, acetate serves as an important source of acetyl coenzyme A (Ac-CoA). However, its exact role and underlying mechanism remain to be investigated.

METHOD

We used chronic social failure stress (CSDS) to induce depression-like phenotype of C57BL/6J mice. The drugs were administered by gavage. We evaluated the depressive symptoms by sucrose preference test, social interaction, tail suspension test and forced swimming test. The dendritic branches and spine density were detected by Golgi staining, mRNA level was analyzed by real-time quantitative RT-PCR, protein expression level was detected by western blot, and the content of Ac-CoA was detected by ELISA kit.

RESULT

The present study found that acetate supplementation significantly improved the depression-like behaviors of mice either in acute forced swimming test (FST) or in CSDS model and that acetate administration enhanced the dendritic branches and spine density of the CA1 pyramidal neurons. Moreover, the down-regulated levels of BDNF and TrkB were rescued in the acetate-treated mice. Of note, chronic acetate treatment obviously lowered the transcription level of HDAC2, HDAC5, HDAC7, HDAC8, increased the transcription level of HAT and P300, and boosted the content of Ac-CoA in the nucleus, which facilitated the acetylation levels of histone H3 and H4.

LIMITATIONS

The effect of acetate supplementation on other brain regions is not further elucidated.

CONCLUSION

These findings indicate that acetate supplementation can produce antidepressant-like effects by increasing histone acetylation and improving synaptic plasticity in hippocampus.

Epigenetic Regulatory Enzymes: mutation Prevalence and Coexistence in Cancers

Epigenetic regulation is an important layer of transcriptional control with the particularity to affect the broad spectrum of genome. Over the years, largely due to the substantial number of recurrent mutations, there have been hundreds of novel driver genes characterized in various cancers. Additionally, the relative contribution of two dysregulated epigenomic entities (DNA methylation and histone modifications) that gradually drive the cancer phenotype remains in the research focus. However, a complex scenario arises when the disease phenotype does not harbor any relevant mutation or an abnormal transcription level. Although the cancer landscape involves the contribution of multiple genetic and non-genetic factors, herein, we discuss specifically the mutation spectrum of epigenetically-related enzymes in cancer. In addition, we address the coexistence of these two epigenetic entities in malignant human diseases, especially cancer. We suggest that the study of epigenetically-related somatic mutations in the early cellular differentiation stage of embryonic development might help to understand their later-staged footprints in the cancer genome. Furthermore, understanding the co-occurrence and/or inverse association of different disease types and redefining the general definition of "healthy" controls could provide insights into the genome reorganization.

Fluoxetine regulates eEF2 activity (phosphorylation) via HDAC1 inhibitory mechanism in an LPS-induced mouse model of depression

BACKGROUND

Selective serotonin reuptaker inhibitors, including fluoxetine, are widely studied and prescribed antidepressants, while their exact molecular and cellular mechanism are yet to be defined. We investigated the involvement of HDAC1 and eEF2 in the antidepressant mechanisms of fluoxetine using a lipopolysaccharide (LPS)-induced depression-like behavior model.

METHODS

For in vivo analysis, mice were treated with LPS (2 mg/kg BW), fluoxetine (20 mg/kg BW), HDAC1 activator (Exifone: 54 mg/kg BW) and NH125 (1 mg/kg BW). Depressive-like behaviors were confirmed via behavior tests including OFT, FST, SPT, and TST. Cytokines were measured by ELISA while Iba-1 and GFAP expression were determined by immunofluorescence. Further, the desired gene expression was measured by immunoblotting. For in vitro analysis, BV2 cell lines were cultured; treated with LPS, exifone, and fluoxetine; collected; and analyzed.

RESULTS

Mice treated with LPS displayed depression-like behaviors, pronounced neuroinflammation, increased HDAC1 expression, and reduced eEF2 activity, as accompanied by altered synaptogenic factors including BDNF, SNAP25, and PSD95. Fluoxetine treatment exhibited antidepressant effects and ameliorated the molecular changes induced by LPS. Exifone, a selective HDAC1 activator, reversed the antidepressant and anti-inflammatory effects of fluoxetine both in vivo and in vitro, supporting a causing role of HDAC1 in neuroinflammation allied depression. Further molecular mechanisms underlying HDAC1 were explored with NH125, an eEF2K inhibitor, whose treatment reduced immobility time, altered pro-inflammatory cytokines, and NLRP3 expression. Moreover, NH125 treatment enhanced eEF2 and GSK3β activities, BDNF, SNAP25, and PSD95 expression, but had no effects on HDAC1.

CONCLUSIONS

Our results showed that the antidepressant effects of fluoxetine may involve HDAC1-eEF2 related neuroinflammation and synaptogenesis.

Epigenetics in bipolar disorder: a critical review of the literature

INTRODUCTION

Bipolar disorder (BD) is a chronic, disabling disease characterised by alternate mood episodes, switching through depressive and manic/hypomanic phases. Mood stabilizers, in particular lithium salts, constitute the cornerstone of the treatment in the acute phase as well as for the prevention of recurrences. The pathophysiology of BD and the mechanisms of action of mood stabilizers remain largely unknown but several pieces of evidence point to gene x environment interactions. Epigenetics, defined as the regulation of gene expression without genetic changes, could be the molecular substrate of these interactions. In this literature review, we summarize the main epigenetic findings associated with BD and response to mood stabilizers.

METHODS

We searched PubMed, and Embase databases and classified the articles depending on the epigenetic mechanisms (DNA methylation, histone modifications and non-coding RNAs).

RESULTS

We present the different epigenetic modifications associated with BD or with mood-stabilizers. The major reported mechanisms were DNA methylation, histone methylation and acetylation, and non-coding RNAs. Overall, the assessments are poorly harmonized and the results are more limited than in other psychiatric disorders (e.g. schizophrenia). However, the nature of BD and its treatment offer excellent opportunities for epigenetic research: clear impact of environmental factors, clinical variation between manic or depressive episodes resulting in possible identification of state and traits biomarkers, documented impact of mood-stabilizers on the epigenome.

CONCLUSION

Epigenetic is a growing and promising field in BD that may shed light on its pathophysiology or be useful as biomarkers of response to mood-stabilizer.

Identification of candidate genetic variants and altered protein expression in neural stem and mature neural cells support altered microtubule function to be an essential component in bipolar disorder

Identification of causative genetic variants leading to the development of bipolar disorder (BD) could result in genetic tests that would facilitate diagnosis. A better understanding of affected genes and pathways is also necessary for targeting of genes that may improve treatment strategies. To date several susceptibility genes have been reported from genome-wide association studies (GWAS), but little is known about specific variants that affect disease development. Here, we performed quantitative proteomics and whole-genome sequencing (WGS). Quantitative proteomics revealed NLRP2 as the most significantly up-regulated protein in neural stem cells and mature neural cells obtained from BD-patient cell samples. These results are in concordance with our previously published transcriptome analysis. Furthermore, the levels of FEZ2 and CADM2 proteins were also significantly differentially expressed in BD compared to control derived cells. The levels of FEZ2 were significantly downregulated in neural stem cells (NSC) while CADM2 was significantly up-regulated in mature neuronal cell culture. Promising novel candidate mutations were identified in the ANK3, NEK3, NEK7, TUBB, ANKRD1, and BRD2 genes. A literature search of candidate variants and deregulated proteins revealed that there are several connections to microtubule function for the molecules putatively involved. Microtubule function in neurons is critical for axon structure and axonal transport. A functional dynamic microtubule is also needed for an advocate response to cellular and environmental stress. If microtubule dynamics is compromised by mutations, it could be followed by deregulated expression forming a possible explanation for the inherited vulnerability to stressful life events that have been proposed to trigger mood episodes in BD patients.

Molecular mechanisms of psychiatric diseases

For most psychiatric diseases, pathogenetic concepts as well as paradigms underlying neuropsychopharmacologic approaches currently revolve around neurotransmitters such as dopamine, serotonin, and norepinephrine. However, despite the fact that several generations of neurotransmitter-based psychotropics including atypical antipsychotics, selective serotonin reuptake inhibitors, and serotonin-norepinephrine reuptake inhibitors are available, the effectiveness of these medications is limited, and relapse rates in psychiatric diseases are relatively high, indicating potential involvement of other pathogenetic pathways. Indeed, recent high-throughput studies in genetics and molecular biology have shown that pathogenesis of major psychiatric illnesses involves hundreds of genes and numerous pathways via such fundamental processes as DNA methylation, transcription, and splicing. Current review summarizes these and other molecular mechanisms of such psychiatric illnesses as schizophrenia, major depressive disorder, and alcohol use disorder and suggests a conceptual framework for future studies.

Epigenetic marks and their relationship with BDNF in the brain of suicide victims

Background

Suicide is a common phenomenon affecting people of all ages. There is a strong relationship between suicidal ideation and depressive disorders. Increasing number of studies suggest that epigenetic modifications in certain brain areas are the main mechanism through which environmental and genetic factors interact with each other contributing to the development of mental disorders. To verify this hypothesis, some epigenetic marks: H3K9/14ac, HDAC2/3, H3K27me2 and Sin3a, as well as p-S421-MeCP2/MeCP2 were examined. On the other hand, BDNF protein level were studied.

Materials and methods

Western blot analysis were performed in the frontal cortex (FCx) and hippocampus (HP) of suicide victims (n = 14) and non-suicidal controls (n = 8). The differences between groups and correlations between selected proteins were evaluated using Mann-Whitney U-test and Spearman’s rank correlation.

Results

Statistically significant decrease in H3K9/14ac (FCx:↓~23%;HP:↓~33%) combined with increase in HDAC3 (FCx:↑~103%;HP:↑~85% in HP) protein levels in suicides compared to the controls was shown. These alterations were accompanied by an increase in H3K27me2 (FCx:↑45%;HP:↑~59%) and Sin3a (HP:↑50%) levels and decrease in p-S421-MeCP2/MeCP2 protein ratio (HP:↓~55%;FCx:↓~27%). Moreover, reduced BDNF protein level (FCx:↓~43%;HP:↓~28%) in suicides was observed. On the other hand, some significant correlations (e.g. between H3K9/14ac and HDAC2 or between BDNF and p-S421-MeCP2/MeCP2) were demonstrated.

Conclusions

Our findings confirm the role of epigenetic component and BDNF protein in suicidal behavior. Lowered BDNF protein level in suicides is probably due to decrease in histone acetylation and increased level of factors related with deacetylation and methylation processes, including MeCP2 factor, which may operate bidirectionally (an activator or inhibitor of transcription).

Effects of Early Life Stress on Epigenetic Changes of the Glucocorticoid Receptor 17 Promoter during Adulthood

Growing evidence suggests that early life stress (ELS) has long-lasting effects on glucocorticoid receptor (GR) expression and behavior via epigenetic changes of the GR exon 1₇ promoter. However, it remains unclear whether ELS regulates histone modifications of the GR exon 1₇ promoter across the life span. We investigated the effects of maternal separation (MS) on histone acetylation and methylation of GR exon 1₇ promoter in the hippocampus, according to the age of adults. Depression-like behavior and epigenetic regulation of GR expression were examined at young and middle adulthood in mice subjected to MS from postnatal day 1 to 21. In the forced swimming test, young adult MS mice showed no effect on immobility time, but middle-aged MS mice significantly increased immobility time. Young adult and middle-aged MS mice showed decreased GR expression. Their two ages showed decreased histone acetylation with increased histone deacetylases (HDAC5) levels, decreased permissive methylation, and increased repressive methylation at the GR exon 1₇ promoter. The extent of changes in gene expression and histone modification in middle adulthood was greater than in young adulthood. These results indicate that MS in early life causes long-term negative effects on behavior via histone modification of the GR gene across the life span.

An epigenome-wide association study of early-onset major depression in monozygotic twins

Major depression (MD) is a debilitating mental health condition with peak prevalence occurring early in life. Genome-wide examination of DNA methylation (DNAm) offers an attractive complement to studies of allelic risk given it can reflect the combined influence of genes and environment. The current study used monozygotic twins to identify differentially and variably methylated regions of the genome that distinguish twins with and without a lifetime history of early-onset MD. The sample included 150 Caucasian monozygotic twins between the ages of 15 and 20 (73% female; Mage = 17.52 SD = 1.28) who were assessed during a developmental stage characterized by relatively distinct neurophysiological changes. All twins were generally healthy and currently free of medications with psychotropic effects. DNAm was measured in peripheral blood cells using the Infinium Human BeadChip 450 K Array. MD associations with early-onset MD were detected at 760 differentially and variably methylated probes/regions that mapped to 428 genes. Genes and genomic regions involved neural circuitry formation, projection, functioning, and plasticity. Gene enrichment analyses implicated genes related to neuron structures and neurodevelopmental processes including cell-cell adhesion genes (e.g., PCDHA genes). Genes previously implicated in mood and psychiatric disorders as well as chronic stress (e.g., NRG3) also were identified. DNAm regions associated with early-onset MD were found to overlap genetic loci identified in the latest Psychiatric Genomics Consortium meta-analysis of depression. Understanding the time course of epigenetic influences during emerging adulthood may clarify developmental phases where changes in the DNA methylome may modulate individual differences in MD risk.

Dietary fiber and its associations with depression and inflammation

Dietary fiber is a crucial component of a healthy diet, with benefits that can be attributed to processes in the gut microbiota and the resulting by-products. Observational studies support associations between dietary fiber intake and depression and inflammation, but the potential mechanisms are poorly understood. This review examines evidence of the effects of dietary fiber on depression and inflammation and considers plausible mechanisms linking dietary fiber and depression, including microbiota-driven modification of gene expression and increased production of neurotransmitters. Additionally, inflammation may mediate the relationship between dietary fiber intake and depression. A high-fiber diet potentially lowers inflammation by modifying both the pH and the permeability of the gut. The resultant reduction in inflammatory compounds may alter neurotransmitter concentrations to reduce symptoms of depression. Further research into the link between dietary fiber intake and inflammation and depression is essential, as findings could potentially provide guidance for improvement in or prevention of inflammatory and depressive disorders.

Epigenetics and depression

The risk for major depression is both genetically and environmentally determined. It has been proposed that epigenetic mechanisms could mediate the lasting increases in depression risk following exposure to adverse life events and provide a mechanistic framework within which genetic and environmental factors can be integrated. Epigenetics refers to processes affecting gene expression and translation that do not involve changes in the DNA sequence and include DNA methylation (DNAm) and microRNAs (miRNAs) as well as histone modifications. Here we review evidence for a role of epigenetics in the pathogenesis of depression from studies investigating DNAm, miRNAs, and histone modifications using different tissues and various experimental designs. From these studies, a model emerges where underlying genetic and environmental risk factors, and interactions between the two, could drive aberrant epigenetic mechanisms targeting stress response pathways, neuronal plasticity, and other behaviorally relevant pathways that have been implicated in major depression.
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Membrane-Associated α-Tubulin Is Less Acetylated in Postmortem Prefrontal Cortex from Depressed Subjects Relative to Controls: Cytoskeletal Dynamics, HDAC6, and Depression

Cytoskeletal proteins and post-translational modifications play a role in mood disorders. Post-translational modifications of tubulin also alter microtubule dynamics. Furthermore, tubulin interacts closely with Gαs, the G-protein responsible for activation of adenylyl cyclase. Postmortem tissue derived from depressed suicide brain showed increased Gαs in lipid-raft domains compared with normal subjects. Gαs, when ensconced in lipid rafts, couples less effectively with adenylyl cyclase to produce cAMP, and this is reversed by antidepressant treatment. A recent in vitro study demonstrated that tubulin anchors Gαs to lipid rafts and that increased tubulin acetylation (due to HDAC6 inhibition) and antidepressant treatment decreased the proportion of Gαs complexed with tubulin. This suggested that deacetylated-tubulin might be more prevalent in depression. This study examined tubulin acetylation in whole-tissue homogenate, plasma membrane, and lipid-raft membrane domains in tissue from normal control subjects, depressed suicides, and depressed nonsuicides (human males/females). While tissue homogenate showed no changes in tubulin acetylation between control, depressed suicides, and depressed nonsuicides, plasma membrane-associated tubulin showed significant decreases in acetylation from depressed suicides and depressed nonsuicides compared with controls. No change was seen in expression of the enzymes responsible for tubulin acetylation or deacetylation. These data suggest that, during depression, membrane-localized tubulin maintains a lower acetylation state, permitting increased sequestration of Gαs in lipid-raft domains, where it is less likely to couple to adenylyl cyclase for cAMP production. Thus, membrane tubulin may play a role in mood disorders, which could be exploited for diagnosis and treatment.SIGNIFICANCE STATEMENT There is little understanding about the molecular mechanisms involved in the development of depression and, in severe cases, suicide. Evidence for the role of microtubule modifications in progression of depressive disorders is emerging. These postmortem data provide strong evidence for membrane tubulin modification leading to reduced efficacy of the G protein, Gαs, in depression. This study reveals a direct link between decreased tubulin acetylation in human depression and the increased localization of Gαs in lipid-raft domains responsible for attenuated cAMP signaling. The evidence presented here suggest a novel diagnostic and therapeutic locus for depression.

Dissecting the Epigenetic Changes Induced by Non-Antipsychotic Mood Stabilizers on Schizophrenia and Affective Disorders: A Systematic Review

BACKGROUND

Epimutations secondary to gene-environment interactions have a key role in the pathophysiology of major psychiatric disorders. In vivo and in vitro evidence suggest that mood stabilizers can potentially reverse epigenetic deregulations found in patients with schizophrenia or mood disorders through mechanisms that are not yet fully understood. However, their activity on epigenetic processes has made them a research target for therapeutic approaches.

METHODS

We conducted a comprehensive literature search of PubMed and EMBASE for studies investigating the specific epigenetic changes induced by non-antipsychotic mood stabilizers (valproate, lithium, lamotrigine, and carbamazepine) in animal models, human cell lines, or patients with schizophrenia, bipolar disorder, or major depressive disorder. Each paper was reviewed for the nature of research, the species and tissue examined, sample size, mood stabilizer, targeted gene, epigenetic changes found, and associated psychiatric disorder. Every article was appraised for quality using a modified published process and those who met a quality score of moderate or high were included.

RESULTS

A total of 2,429 records were identified; 1,956 records remained after duplicates were removed and were screened via title, abstract and keywords; 129 records were selected for full-text screening and a remaining of 38 articles were included in the qualitative synthesis. Valproate and lithium were found to induce broader epigenetic changes through different mechanisms, mainly DNA demethylation and histones acetylation. There was less literature and hence smaller effects attributable to lamotrigine and carbamazepine could be associated overall with the small number of studies on these agents. Findings were congruent across sample types.

CONCLUSIONS

An advanced understanding of the specific epigenetic changes induced by classic mood stabilizers in patients with major psychiatric disorders will facilitate personalized interventions. Further related drug discovery should target the induction of selective chromatin remodeling and gene-specific expression effects.

Behavioral Alterations in Mice Carrying Homozygous HDAC4 A778T Missense Mutation Associated With Eating Disorder

Eating disorders (EDs) are serious mental illnesses thought to arise from the complex gene-environment interactions. DNA methylation patterns in histone deacetylase 4 (HDAC4) locus have been associated with EDs and we have previously identified a missense mutation in the HDAC4 gene (HDAC4^A786T) that increases the risk of developing an ED. In order to evaluate the biological consequences of this variant and establish a useful mouse model of EDs, here we performed behavioral characterization of mice homozygous for Hdac4^A778T (corresponding to human HDAC4^A786T) that were further backcrossed onto C57BL/6 background. When fed high-fat diet, male, but not female, homozygous mice showed a trend toward decreased weight gain compared to their wild-type littermates. Behaviorally, male, but not female, homozygous mice spent less time in eating and exhibited reduced motivation to work for palatable food and light phase-specific decrease in locomotor activity. Additionally, homozygous Hdac4^A778T female, but not male, mice display social subordination when subjected to a tube dominance test. Collectively, these results reveal a complex sex- and circadian-dependent role of ED-associated Hdac4^A778T mutation in affecting mouse behaviors. Homozygous Hdac4^A778T mice could therefore be a useful animal model to gain insight into the neurobiological basis of EDs.

Molecular adaptations of the blood-brain barrier promote stress resilience vs. depression

Preclinical and clinical studies suggest that inflammation and vascular dysfunction contribute to the pathogenesis of major depressive disorder (MDD). Chronic social stress alters blood-brain barrier (BBB) integrity through loss of tight junction protein claudin-5 (cldn5) in male mice, promoting passage of circulating proinflammatory cytokines and depression-like behaviors. This effect is prominent within the nucleus accumbens, a brain region associated with mood regulation; however, the mechanisms involved are unclear. Moreover, compensatory responses leading to proper behavioral strategies and active resilience are unknown. Here we identify active molecular changes within the BBB associated with stress resilience that might serve a protective role for the neurovasculature. We also confirm the relevance of such changes to human depression and antidepressant treatment. We show that permissive epigenetic regulation of cldn5 expression and low endothelium expression of repressive cldn5-related transcription factor foxo1 are associated with stress resilience. Region- and endothelial cell-specific whole transcriptomic analyses revealed molecular signatures associated with stress vulnerability vs. resilience. We identified proinflammatory TNFα/NFκB signaling and hdac1 as mediators of stress susceptibility. Pharmacological inhibition of stress-induced increase in hdac1 activity rescued cldn5 expression in the NAc and promoted resilience. Importantly, we confirmed changes in HDAC1 expression in the NAc of depressed patients without antidepressant treatment in line with CLDN5 loss. Conversely, many of these deleterious CLDN5-related molecular changes were reduced in postmortem NAc from antidepressant-treated subjects. These findings reinforce the importance of considering stress-induced neurovascular pathology in depression and provide therapeutic targets to treat this mood disorder and promote resilience.

Ketamine in Bipolar Disorder: A Review

Bipolar disorder (BD) is a psychiatric illness associated with high morbidity, mortality and suicide rate. It has neuroprogressive course and a high rate of treatment resistance. Hence, there is an unquestionable need for new BD treatment strategies. Ketamine appears to have rapid antidepressive and antisuicidal effects. Since most of the available studies concern unipolar depression, here we present a novel insight arguing that ketamine might be a promising treatment for bipolar disorder.

Correlations Between SIRT Genetic Polymorphisms and Postpartum Depressive Symptoms in Chinese Parturients Who Had Undergone Cesarean Section

OBJECTIVE

To investigate the association of genetic polymorphisms of SIRT with postpartum depressive symptoms and analyze the risk factors for postpartum depressive symptoms in women following cesarean section.

METHODS

A total of 368 Chinese woman undergoing cesarean section were enrolled in this study. A cutoff of ≥10 for the Edinburgh Postnatal Depression Scale identified postpartum depressive symptoms. Genotypes of SIRT1, SIRT 2, and SIRT 6 were determined using Sequenom MassArray single-nucleotide polymorphism (SNP) analysis. We analyzed the contribution of genetic factors (SNPs, linkage disequilibrium, and haplotype) to postpartum depressive symptoms and performed logistic regression analysis to identify all potential risk factors for postpartum depressive symptoms and define interactions between genetic and environmental factors.

RESULTS

The incidence of postpartum depressive symptoms was 18.7% in this cohort. Univariate analysis suggested that SIRT2 polymorphism at rs2873703 (TT genotype) and rs4801933 ((TT genotype) and SIRT6 polymorphism at rs350846 (CC genotype) and rs107251 (TT genotype) were significantly correlated with the occurrence of postpartum depressive symptoms (p<0.05). Linkage disequilibrium was identified between SIRT6 polymorphisms rs350846 and rs107251. Incidence of postpartum depressive symptoms in cesarean-section parturients with SIRT2 haplotype CCC was decreased (OR 0.407, 95% CI 0.191-0.867; p=0.016). SIRT2 polymorphisms rs2873703 and rs4801933 were multiply collinear. Logistic regression analysis showed that SIRT2 polymorphism at rs2873703 (TT genotype) and rs4801933 (TT genotype), domestic violence, stress during pregnancy, and depressive prenatal mood were risk factors for postpartum depressive symptoms (p<0.05).

CONCLUSION

Pregnant women with SIRT2 genotypes rs2873703 TT and rs4801933 TT and experiencing domestic violence, stress during pregnancy, and prenatal depression are more likely to suffer from postpartum depressive symptoms.

Antidepressant mechanisms of venlafaxine involving increasing histone acetylation and modulating tyrosine hydroxylase and tryptophan hydroxylase expression in hippocampus of depressive rats

Venlafaxine (VEN) is a widely used antidepressant as a serotonin-reuptake and norepinephrine-reuptake inhibitor. It is used primarily in depression, especially with generalized anxiety disorder or chronic pain. This medicine is of interest because its mechanisms involved multiple aspects. In the current study, the antidepressant action of VEN was investigated by studying the histone acetylation and expression of tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH) in rats exposed to chronic unpredicted stress (CUS) for 28 days. Male Sprague-Dawley rats were divided into a control group, VEN-treated control group, CUS group, and VEN-treated CUS group. VEN (23.4 mg/kg once daily) was administered to rats by intragastric gavage, whereas the same volume of vehicle was given to rats in the control and model groups. Rat behaviors, acetylated H3 at lysine 9 (acH3K9), acetylated H3 at lysine 14 (acH3K14), acetylated H4 at lysine 12 (acH4K12), histone deacetylase 5, and TH and TPH expression in the hippocampus were determined. Chronic VEN treatment significantly relieved the anxiety- and depression-like behaviors, prevented the increase of histone deacetylase 5 expression and decrease of acH3K9 level, and promoted TH and TPH protein expression in the hippocampus of CUS rats. The results suggest that the preventive antidepressant mechanism of VEN is partly involved in the blocking effects on histone de-acetylated modification and then increasing TH, TPH expression.