Sex-specific transcriptional signatures in human depression

Comparative analysis of hippocampal transcriptional features between major depressive disorder patients and animal models

BACKGROUND

Major depressive disorder (MDD) is a psychiatric disorder caused by various etiologies. Chronic stress models are used to simulate the heterogeneous pathogenic processes of depression. However, few studies have compared transcriptional features between stress models and MDD patients.

METHODS

We generated hippocampal transcriptional profiles of the chronic social defeat model by RNA sequencing and downloaded raw data of the same brain region from public databases of the chronic unpredictable mild stress model, the learned helplessness model, and MDD patients. Differential expression and gene co-expression analyses were integrated to compare transcriptional features between stress models and MDD patients.

RESULTS

Each stress model shared 11.4% to 16.3% of differentially expressed genes with MDD patients. Functional analysis at the gene expression level identified altered ensheathment of neurons in both stress models and MDD patients. At the gene network level, each stress model shared 20.9% to 41.6% of co-expressed genes with MDD patients. Functional analysis based on these genes found that axon guidance signaling is the most significantly enriched pathway that was shared by all stress models and MDD patients.

LIMITATIONS

This study was limited by considering only a single brain region and a single sex of stress model animals.

CONCLUSIONS

Our results show that hippocampal transcriptional features of stress models partially overlap with those of MDD patients. The canonical pathways of MDD patients, including ensheathment of neurons, PTEN signaling, and axonal guidance signaling, were shared with all stress models. Our findings provide further clues to understand the molecular mechanisms of depression.

Uncovering microglial pathways driving sex-specific neurobiological effects in stress and depression

Women suffer from major depressive disorder (MDD) more often than men and report greater MDD symptom severity. Mounting evidence suggests that sex differences in MDD may be driven, in part, by sex-specific neurobiological mechanisms. Chronic stress is a significant risk factor in MDD, and preclinical rodent models show differential patterns of stress-induced neural remodeling and cognitive-behavioral dysfunction in males and females. For instance, chronic stress leads to synapse loss in the medial prefrontal cortex in male rodents yet has either no effect on- or increases-synapse number in females. Recent reports have implicated microglia, the immune cells of the brain, in MDD, and findings demonstrate sex-specific microglial signatures in both preclinical stress models and MDD patients. Given that microglia can remodel neural architecture, modulate synaptic transmission, and affect subsequent changes in behavior, it is plausible that microglial pathways contribute to differential stress effects on neuroplasticity and function in males and females. As such, this review examines the evidence for sex-specific microglia-neuron interactions in preclinical stress models and in patients with MDD. Discoveries highlighted herein demonstrate divergent microglial contributions in males and females and suggest that future studies investigating stress-linked disorders should be guided by sex-dependent neurobiological and behavioral findings. Examining these pathways represents a clear avenue toward both a richer understanding of brain, behavior, and immunity, and innovative psychoneuroimmunology-based applications in personalized medicine.

Cerebral perfusion in depression: Relationship to sex, dehydroepiandrosterone sulfate and depression severity

BACKGROUND

Major depressive disorder (MDD) is a leading cause of disease burden and shows a marked sexual dimorphism. Previous studies reported changes in cerebral perfusion in MDD, an association between perfusion and dehydroepiandrosterone sulfate (DHEAS) levels, and large sex differences in perfusion. This study examines whether perfusion and DHEAS might mediate the link between sex and depressive symptoms in a large, unmedicated community sample.

METHODS

The sample included 203 healthy volunteers and 79 individuals with past or current MDD. Depression severity was assessed with the Hamilton Depression Scale (HAM-D) and Montgomery-Asberg Depression Rating Scale (MADRS). 3 T MRI perfusion data were collected with a pseudocontinuous arterial spin labelling sequence and DHEAS was measured in serum by LC-MS/MS.

RESULTS

Large sex differences in perfusion were observed (p < 0.001). Perfusion was negatively correlated with DHEAS (r = -0.23, p < 0.01, n = 250) and with depression severity (HAM-D: r = -0.17, p = 0.01, n = 242; partial Spearman correlation, controlling for age and sex), but not with anxiety. A significant sex*perfusion interaction on depression severity was observed. In women, perfusion showed more pronounced negative correlations with depressive symptoms, with absent or, in the case of the MADRS, opposite effects observed in men. A mediation analysis identified DHEAS and perfusion as mediating variables influencing the link between sex and the HAM-D score.

CONCLUSION

Perfusion was linked to depression severity, with the strongest effects observed in women. Perfusion and the neurosteroid DHEAS appear to mediate the link between sex and HAM-D scores, suggesting that inter-individual differences in perfusion and DHEAS levels may contribute to the sexual dimorphism in depression.

Individual history of winning and hierarchy landscape influence stress susceptibility in mice

Social hierarchy formation is strongly evolutionarily conserved. Across species, rank within social hierarchy has large effects on health and behavior. To investigate the relationship between social rank and stress susceptibility, we exposed ranked male and female mice to social and non-social stressors and manipulated social hierarchy position. We found that rank predicts same sex social stress outcomes: dominance in males and females confers resilience while subordination confers susceptibility. Pre-existing rank does not predict non-social stress outcomes in females and weakly does so in males, but rank emerging under stress conditions reveals social interaction deficits in male and female subordinates. Both history of winning and rank of cage mates affect stress susceptibility in males: rising to the top rank through high mobility confers resilience and mice that lose dominance lose stress resilience, although gaining dominance over a subordinate animal does not confer resilience. Overall, we have demonstrated a relationship between social status and stress susceptibility, particularly when taking into account individual history of winning and the overall hierarchy landscape in male and female mice.

Identification of transcriptome alterations in the prefrontal cortex, hippocampus, amygdala and hippocampus of suicide victims

Suicide is one of the leading causes of death globally for all ages, and as such presents a very serious problem for clinicians worldwide. However, the underlying neurobiological pathology remains to a large extent unknown. In order to address this gap, we have carried out a genome-wide investigation of the gene expression in the amygdala, hippocampus, prefrontal cortex and thalamus in post-mortem brain samples obtained from 20 suicide completers and 7 control subjects. By KEGG enrichment analysis indicated we identified novel clusters of downregulated pathways involved in antigen neutralization and autoimmune thyroid disease (amygdala, thalamus), decreased axonal plasticity in the hippocampus. Two upregulated pathways were involved in neuronal death in the hippocampus and olfactory transduction in the thalamus and the prefrontal cortex. Autoimmune thyroid disease pathway was downregulated only in females. Metabolic pathways involved in Notch signaling amino acid metabolism and unsaturated lipid synthesis were thalamus-specific. Suicide-associated changes in the expression of several genes and pseudogenes that point to various functional mechanisms possibly implicated in the pathology of suicide. Two genes (SNORA13 and RNU4-2) involved in RNA processing were common to all brain regions analyzed. Most of the identified gene expression changes were related to region-specific dysregulated manifestation of genetic and epigenetic mechanisms underlying neurodevelopmental disorders (SNORD114-10, SUSd1), motivation, addiction and motor disorders (CHRNA6), long-term depression (RAB3B), stress response, major depression and schizophrenia (GFAP), signal transduction at the neurovascular unit (NEXN) and inhibitory neurotransmission in spatial learning, neural plasticity (CALB2; CLIC6, ENPP1). Some of the differentially expressed genes were brain specific non-coding RNAs involved in the regulation of translation (SNORA13). One, (PARM1) is a potential oncogene and prognostic biomarker for colorectal cancer with no known function in the brain. Disturbed gene expression involved in antigen neutralization, autoimmunity, neural plasticity, stress response, signal transduction at the neurovascular unit, dysregulated nuclear RNA processing and translation and epigenetic imprinting signatures is associated with suicide and point to regulatory non-coding RNAs as potential targets of new drugs development.

Comparing axon regeneration in male and female mice after peripheral nerve injury

Axons in the adult mammalian central nervous system fail to regenerate after injury. By contrast, spontaneous axon regeneration occurs in the peripheral nervous system (PNS) due to a supportive PNS environment and an increase in the intrinsic growth potential induced by injury via cooperative activation of multifaceted biological pathways. This study compared axon regeneration and injury responses in C57BL/6 male and female mice after sciatic nerve crush (SNC) injury. The extent of axon regeneration in vivo was indistinguishable in male and female mice when observed at 3 days after SNC injury, and primary dorsal root ganglion (DRG) neurons from injured, male and female mice extended axons to a similar length. Moreover, the induction of selected regeneration-associated genes (RAGs), such as Atf3, Sprr1a, Gap43, Sox11, Jun, Gadd45a, and Smad1 were comparable in male and female DRGs when assessed by quantitative real-time reverse transcription polymerase chain reaction. Furthermore, the RNA-seq analysis of male and female DRGs revealed that differentially expressed genes (DEGs) in SNC groups compared to sham-operated groups included many common genes associated with neurite outgrowth. However, we also found that a large number of genes in the DEGs were sex dependent, implicating the involvement of distinct gene regulatory network in the two sexes following peripheral nerve injury. In conclusion, we found that male and female mice mounted a comparable axon regeneration response and many RAGs were commonly induced in response to SNC. However, given that many DEGs were sex-dependently expressed, future studies are needed to investigate whether they contribute to peripheral axon regeneration, and if so, to what extent.

Sex-Specific Retinal Anomalies Induced by Chronic Social Defeat Stress in Mice

Major depressive disorder (MDD) is one of the most common consequences of chronic stress. Still, there is currently no reliable biomarker to detect individuals at risk to develop the disease. Recently, the retina emerged as an effective way to investigate psychiatric disorders using the electroretinogram (ERG). In this study, cone and rod ERGs were performed in male and female C57BL/6 mice before and after chronic social defeat stress (CSDS). Mice were then divided as susceptible or resilient to stress. Our results suggest that CSDS reduces the amplitude of both oscillatory potentials and a-waves in the rods of resilient but not susceptible males. Similar effects were revealed following the analysis of the cone b-waves, which were faster after CSDS in resilient mice specifically. In females, rod ERGs revealed age-related changes with no change in cone ERGs. Finally, our analysis suggests that baseline ERG can predict with an efficacy up to 71% the expression of susceptibility and resilience before stress exposition in males and females. Overall, our findings suggest that retinal activity is a valid biomarker of stress response that could potentially serve as a tool to predict whether males and females will become susceptible or resilient when facing CSDS.

Expression Biomarkers of Pharmacological Treatment Outcomes in Women with Unipolar and Bipolar Depression

INTRODUCTION

This study aimed to find the expression biomarkers of pharmacological treatment response in a naturalistic hospital setting. Through gene expression profiling, we were able to find differentially-expressed genes (DEGs) in unipolar (UD) and bipolar (BD) depressed women.

METHODS

We performed gene expression profiling in hospitalized women with unipolar (n=24) and bipolar depression (n=32) who achieved clinical improvement after pharmacological treatment (without any restriction). To identify DEGs in peripheral blood mononuclear cells (PBMCs), we used the SurePrint G3 Microarray and GeneSpring software.

RESULTS

After pharmacological treatment, UD and BD varied in the number of regulated genes and ontological pathways. Also, the pathways of neurogenesis and synaptic transmission were significantly up-regulated. Our research focused on DEGs with a minimum fold change (FC) of more than 2. For both types of depression, 2 up-regulated genes, OPRM1 and CELF4 (p=0.013), were significantly associated with treatment response (defined as a 50% reduction on the Hamilton Depression Rating Scale [HDRS]). We also uncovered the SHANK3 (p=0.001) gene that is unique for UD and found that the RASGRF1 (p=0.010) gene may be a potential specific biomarker of treatment response for BD.

CONCLUSION

Based on transcriptomic profiling, we identified potential expression biomarkers of treatment outcomes for UD and BD. We also proved that the Ras-GEF pathway associated with long-term memory, female stress response, and treatment response modulation in animal studies impacts treatment efficacy in patients with BD. Further studies focused on the outlined genes may help provide predictive markers of treatment outcomes in UD and BD.

MicroRNA-195 rescues ApoE4-induced cognitive deficits and lysosomal defects in Alzheimer's disease pathogenesis

Our recent findings link the apolipoprotein E4 (ApoE4)-specific changes in brain phosphoinositol biphosphate (PIP2) homeostasis to the susceptibility of developing Alzheimer's Disease (AD). In the present study, we have identified miR-195 as a top micro-RNA candidate involved in the ApoE/PIP2 pathway using miRNA profiles in human ROSMAP datasets and mouse microarray studies. Further validation studies have demonstrated that levels of miR-195 are significantly lower in human brain tissue of ApoE4+/- patients with clinical diagnosis of mild cognitive impairment (MCI) or early AD when compared to ApoE4-/- subjects. In addition, brain miR-195 levels are reduced along with disease progression from normal aging to early AD, and cerebrospinal fluid (CSF) miR-195 levels of MCI subjects are positively correlated with cognitive performances as measured by mini-mental status examination (MMSE) and negatively correlated with CSF tau levels, suggesting the involvement of miR-195 in early development of AD with a potential impact on cognition. Similar differences in miR-195 levels are seen in ApoE4+/+ mouse hippocampal brain tissue and cultured neurons when compared to ApoE3+/+ counterparts. Over-expressing miR-195 reduces expression levels of its top predicted target synaptojanin 1 (synj1), a brain PIP2-degrading enzyme. Furthermore, elevating miR-195 ameliorates cognitive deficits, amyloid plaque burden, and tau hyper-phosphorylation in ApoE4+/+ mice. In addition, elevating miR-195 rescues AD-related lysosomal defects in inducible pluripotent stem cells (iPSCs)-derived brain cells of ApoE4+/+ AD subjects while inhibiting miR-195 exacerbates these phenotypes. Together, our data uncover a novel regulatory mechanism of miR-195 targeted at ApoE4-associated brain PIP2 dyshomeostasis, cognitive deficits, and AD pathology.

The Effect of Individual Musculoskeletal Conditions on Depression: Updated Insights From an Irish Longitudinal Study on Aging

Few longitudinal studies have systematically investigated whether or how individual musculoskeletal conditions (IMCs) convey risks for negative psychological health outcomes, and approaches to assess such risk in the older population are lacking. In this Irish nationally representative longitudinal prospective study of 6,715 individuals aged 50 and above, machine learning algorithms and various models, including mediation models, were employed to elaborate the underlying mechanisms of IMCs leading to depression and to develop an IMC-induced negative psychological risk (IMCPR) classification approach. Resultantly, arthritis [odds ratio (95% confidence interval): 2.233 (1.700-2.927)], osteoporosis [1.681 (1.133-2.421)], and musculoskeletal chronic pain [MCP, 2.404 (1.838-3.151)] were found to increase the risk of depression after 2 years, while fracture and joint replacement did not. Interestingly, mediation models further demonstrated that arthritis per se did not increase the risk of depression; such risk was augmented only when arthritis-induced restrictions of activities (ARA) existed [proportion of mediation: 316.3% (ARA of usual), 213.3% (ARA of social and leisure), and 251.3% (ARA of sleep)]. The random forest algorithm attested that osteoarthritis, not rheumatoid arthritis, contributed the most to depressive symptoms. Moreover, bone mineral density was negatively associated with depressive symptoms. Systemic pain contributed the most to the increased risk of depression, followed by back, knee, hip, and foot pain (mean Gini-Index: 3.778, 2.442, 1.980, 1.438, and 0.879, respectively). Based on the aforementioned findings, the IMCPR classification approach was developed using an interpretable machine learning model, which stratifies participants into three grades. Among the IMCPR grades, patients with a grade of "severe" had higher odds of depression than those with a "mild" [odds ratio (95% confidence interval): 4.055 (2.907-5.498)] or "moderate" [3.584 (2.101-5.883)] grade. Females with a "severe" grade had higher odds of depression by 334.0% relative to those with a "mild" grade, while males had a relative risk of 258.4%. In conclusion, the present data provide systematic insights into the IMC-induced depression risk and updated the related clinical knowledge. Furthermore, the IMCPR classification approach could be used as an effective tool to evaluate this risk.

Depression is associated with hippocampal volume loss in adults with HIV

Depressive symptoms are more prevalent in persons with HIV (PWH) than HIV-uninfected individuals. In HIV-uninfected individuals, depression has been associated with atrophy in the hippocampus and other brain regions. In the present study, we investigated the impact of depression on brain structure in PWH. One hundred PWH participated in a cross-sectional study (56.6 ± 6.4 yrs, range 41-70 yrs, 24 females, 63 African Americans). The Beck's Depression Inventory-II (BDI-II) was used to assess depressive symptoms. Structural MRI images were collected. Both the voxel-based morphometry (VBM) technique and a region of interest (ROI) based approach were used to examine the relationship between hippocampal gray matter volume (GMv) and depressive symptoms. The impact of HIV CD4 nadir and antidepressants was also investigated. Both VBM and ROI approaches revealed that higher BDI-II scores (implicating more severe depressive symptoms) were associated with loss of hippocampal GMv, especially in the right hippocampus and the right entorhinal cortex. Low CD4 nadir predicted additional hippocampal volume loss independent of depressive symptoms. Taking antidepressants did not have a detectable effect on hippocampal volume. In summary, having more depressive symptoms is associated with smaller hippocampal volume in PWH, and a history of severe immunosuppression (i.e., low CD4 nadir) correlates with additional hippocampal volume reduction. However, the impact of depression on hippocampal volume may be independent of HIV-disease severity such as low CD4 nadir.

Defining Valid Chronic Stress Models for Depression With Female Rodents

Women are twice as likely to experience depression than men, yet until recently, preclinical studies in rodents have focused almost exclusively on males. As interest in sex differences and sex-specific mechanisms of stress susceptibility increases, chronic stress models for inducing depression-relevant behavioral and physiological changes in male rodents are being applied to females, and several new models have emerged to include both males and females, yet not all models have been systematically validated in females. An increasing number of researchers seek to include female rodents in their experimental designs, asking the question "what is the ideal chronic stress model for depression in females?" We review criteria for assessing female model validity in light of key research questions and the fundamental distinction between studying sex differences and studying both sexes. In overviewing current models, we explore challenges inherent to establishing an ideal female chronic stress model, with particular emphasis on the need for standardization and adoption of validated behavioral tests sensitive to stress effects in females. Taken together, these considerations will empower female chronic stress models to provide a better understanding of stress susceptibility and allow the development of efficient sex-specific treatments.

Chronic Stress Induces Sex-Specific Functional and Morphological Alterations in Corticoaccumbal and Corticotegmental Pathways

BACKGROUND

The medial prefrontal cortex (mPFC) is part of a complex circuit controlling stress responses by sending projections to different limbic structures including the nucleus accumbens (NAc) and ventral tegmental area (VTA). However, the impact of chronic stress on NAc- and VTA-projecting mPFC neurons is still unknown, and the distinct contribution of these pathways to stress responses in males and females is unclear.

METHODS

Behavioral stress responses were induced by 21 days of chronic variable stress in male and female C57BL/6NCrl mice. An intersectional viral approach was used to label both pathways and assess the functional, morphological, and transcriptional adaptations in NAc- and VTA-projecting mPFC neurons in stressed males and females. Using chemogenetic approaches, we modified neuronal activity of NAc-projecting mPFC neurons to decipher their contribution to stress phenotypes.

RESULTS

Chronic variable stress induced depressive-like behaviors in males and females. NAc- and VTA-projecting mPFC neurons exhibited sex-specific functional, morphological, and transcriptional alterations. The functional changes were more severe in females in NAc-projecting mPFC neurons, while males exhibited more drastic reductions in dendritic complexity in VTA-projecting mPFC neurons after chronic variable stress. Finally, chemogenetic overactivation of the corticoaccumbal pathway triggered anxiety and behavioral despair in both sexes, while its inhibition rescued the phenotype only in females.

CONCLUSIONS

Our results suggest that stress responses in males and females result from pathway-specific changes in the activity of transcriptional programs controlling the morphological and synaptic properties of corticoaccumbal and corticotegmental pathways in a sex-specific fashion.

Regulation of impulsive and aggressive behaviours by a novel lncRNA

High impulsive and aggressive traits associate with poor behavioural self-control. Despite their importance in predicting behavioural negative outcomes including suicide, the molecular mechanisms underlying the expression of impulsive and aggressive traits remain poorly understood. Here, we identified and characterized a novel long noncoding RNA (lncRNA), acting as a regulator of the monoamine oxidase A (MAOA) gene in the brain, and named it MAOA-associated lncRNA (MAALIN). Our results show that in the brain of suicide completers, MAALIN is regulated by a combination of epigenetic mechanisms including DNA methylation and chromatin modifications. Elevated MAALIN in the dentate gyrus of impulsive-aggressive suicides was associated with lower MAOA expression. Viral overexpression of MAALIN in neuroprogenitor cells decreased MAOA expression while CRISPR-mediated knock out resulted in elevated MAOA expression. Using viral-mediated gene transfer, we confirmed that MAALIN in the hippocampus significantly decreases MAOA expression and exacerbates the expression of impulsive-aggressive behavioural traits in CD1 aggressive mice. Overall, our findings suggest that variations in DNA methylation mediate the differential expression of a novel lncRNA that acts on MAOA expression to regulate impulsive-aggressive behaviours.

Sperm Transcriptional State Associated with Paternal Transmission of Stress Phenotypes

Paternal stress can induce long-lasting changes in germ cells potentially propagating heritable changes across generations. To date, no studies have investigated differences in transmission patterns between stress-resilient and stress-susceptible mice. We tested the hypothesis that transcriptional alterations in sperm during chronic social defeat stress (CSDS) transmit increased susceptibility to stress phenotypes to the next generation. We demonstrate differences in offspring from stressed fathers that depend on paternal category (resilient vs susceptible) and offspring sex. Importantly, artificial insemination (AI) reveals that sperm mediates some of the behavioral phenotypes seen in offspring. Using RNA-sequencing (RNA-seq), we report substantial and distinct changes in the transcriptomic profiles of sperm following CSDS in susceptible versus resilient fathers, with alterations in long noncoding RNAs (lncRNAs) predominating especially in susceptibility. Correlation analysis revealed that these alterations were accompanied by a loss of regulation of protein-coding genes by lncRNAs in sperm of susceptible males. We also identify several co-expression gene modules that are enriched in differentially expressed genes (DEGs) in sperm from either resilient or susceptible fathers. Taken together, these studies advance our understanding of intergenerational epigenetic transmission of behavioral experience.SIGNIFICANCE STATEMENT This manuscript contributes to the complex factors that influence the paternal transmission of stress phenotypes. By leveraging the segregation of males exposed to chronic social defeat stress (CSDS) into either resilient or susceptible categories we were able to identify the phenotypic differences in the paternal transmission of stress phenotypes across generations between the two lineages. Importantly, this work also alludes to the significance of both long noncoding RNAs (lncRNAs) and protein coding genes (PCGs) mediating the paternal transmission of stress. The knowledge gained from these data are of particular interest in understanding the risk for the development of psychiatric disorders such as anxiety and depression.

How Stress Shapes Neuroimmune Function: Implications for the Neurobiology of Psychiatric Disorders

Chronic stress causes physiological and hormonal adaptations that lead to neurobiological consequences and behavioral and cognitive impairments. In particular, chronic stress has been shown to drive reduced neurogenesis and altered synaptic plasticity in brain regions that regulate mood and motivation. The neurobiological and behavioral effects of stress resemble the pathophysiology and symptoms observed in psychiatric disorders, suggesting that there are similar underlying mechanisms. Accumulating evidence indicates that neuroimmune systems, particularly microglia, have a critical role in regulating the neurobiology of stress. Preclinical models indicate that chronic stress provokes changes in microglia phenotype and increases inflammatory cytokine signaling, which affects neuronal function and leads to synaptic plasticity deficits and impaired neurogenesis. More recent work has shown that microglia can also phagocytose neuronal elements and contribute to structural remodeling of neurons in response to chronic stress. In this review we highlight work by the Duman research group (as well as others) that has revealed how chronic stress shapes neuroimmune function and, in turn, how inflammatory mediators and microglia contribute to the neurobiological effects of chronic stress. We also provide considerations to engage the therapeutic potential of neuroimmune systems, with the goal of improving treatment for psychiatric disorders.

Stress and Its Impact on the Transcriptome

Exposure to stress during the course of a lifetime is inevitable in the animal kingdom. It is the response to stress, the valence of the exposure, and the developmental time point that largely determine the consequences to the initial and subsequent exposures. The versatility of transcriptomic methods to yield rich, high-resolution, information-laden datasets from entire brain regions to single cells makes it a powerful approach to investigate the effects of stress from several angles. Dysregulation of the transcriptome is now a phenotypic signature of many neuropsychiatric disorders. New insight has been gained from examining stress-induced changes in gene expression at a global scale. Human postmortem datasets from depression and posttraumatic stress disorder studies have identified major gene expression changes in the diseased brain, including sex-specific changes and marked differences in male and female molecular profiles for the same disorder. Extensions of this work into animal models have explored the impact of transcriptomic dysregulation on early-life stress, chronic stress, and transgenerational impact of stress. Here, we explore the findings of human postmortem genomic studies of neuropsychiatric disorders and comparable animal models through the lens of transcriptomic dysregulation and how these findings have contributed to our understanding of stress.

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.

What Do the Animal Studies of Stress Resilience Teach Us?

Long-lasting stress factors, both biological and psychological, are commonly accepted as the main cause of depressive disorders. Several animal models, using various stressful stimuli, have been used to find biochemical and molecular alterations that could help us understand the etiopathogenesis of depression. However, recent sophisticated studies indicate that the most frequently used animal models of stress only capture a portion of the molecular features associated with complex human disorders. On the other hand, some of these models generate groups of animals resilient to stress. Studies of the mechanisms of stress resilience bring us closer to understanding the process of adapting to aversive stimuli and the differences between stress-susceptible vs. resilient phenotypes. Especially interesting in this context is the chronic mild stress (CMS) experimental paradigm, most often using rats. Studies using this animal model have revealed that biochemical (e.g., the dopamine D2 receptor) and molecular (e.g., microRNA) alterations are dynamic (i.e., depend on stress duration, 2 vs. 7 weeks) and much more pronounced in stress-resilient than stress-susceptible groups of animals. We strongly suggest that studies aimed at understanding the molecular and biochemical mechanisms of depression must consider these dynamics. A good candidate to serve as a biomarker in such studies might be serum microRNA, since it can be obtained relatively easily from living individuals at various time points.

Functional Contribution of the Medial Prefrontal Circuitry in Major Depressive Disorder and Stress-Induced Depressive-Like Behaviors

Despite decades of research on the neurobiology of major depressive disorder (MDD), the mechanisms underlying its expression remain unknown. The medial prefrontal cortex (mPFC), a hub region involved in emotional processing and stress response elaboration, is highly impacted in MDD patients and animal models of chronic stress. Recent advances showed alterations in the morphology and activity of mPFC neurons along with profound changes in their transcriptional programs. Studies at the circuitry level highlighted the relevance of deciphering the contributions of the distinct prefrontal circuits in the elaboration of adapted and maladapted behavioral responses in the context of chronic stress. Interestingly, MDD presents a sexual dimorphism, a feature recognized in the molecular field but understudied on the circuit level. This review examines the recent literature and summarizes the contribution of the mPFC circuitry in the expression of MDD in males and females along with the morphological and functional alterations that change the activity of these neuronal circuits in human MDD and animal models of depressive-like behaviors.

Splicing and editing of ionotropic glutamate receptors: a comprehensive analysis based on human RNA-Seq data

Ionotropic glutamate receptors (iGluRs) play key roles for signaling in the central nervous system. Alternative splicing and RNA editing are well-known mechanisms to increase iGluR diversity and to provide context-dependent regulation. Earlier work on isoform identification has focused on the analysis of cloned transcripts, mostly from rodents. We here set out to obtain a systematic overview of iGluR splicing and editing in human brain based on RNA-Seq data. Using data from two large-scale transcriptome studies, we established a workflow for the de novo identification and quantification of alternative splice and editing events. We detected all canonical iGluR splice junctions, assessed the abundance of alternative events described in the literature, and identified new splice events in AMPA, kainate, delta, and NMDA receptor subunits. Notable events include an abundant transcript encoding the GluA4 amino-terminal domain, GluA4-ATD, a novel C-terminal GluD1 (delta receptor 1) isoform, GluD1-b, and potentially new GluK4 and GluN2C isoforms. C-terminal GluN1 splicing may be controlled by inclusion of a cassette exon, which shows preference for one of the two acceptor sites in the last exon. Moreover, we identified alternative untranslated regions (UTRs) and species-specific differences in splicing. In contrast, editing in exonic iGluR regions appears to be mostly limited to ten previously described sites, two of which result in silent amino acid changes. Coupling of proximal editing/editing and editing/splice events occurs to variable degree. Overall, this analysis provides the first inventory of alternative splicing and editing in human brain iGluRs and provides the impetus for further transcriptome-based and functional investigations.

Stress-induced alterations of mesocortical and mesolimbic dopaminergic pathways

Our ability to develop the cognitive strategies required to deal with daily-life stress is regulated by region-specific neuronal networks. Experimental evidence suggests that prolonged stress in mice induces depressive-like behaviors via morphological, functional and molecular changes affecting the mesolimbic and mesocortical dopaminergic pathways. Yet, the molecular interactions underlying these changes are still poorly understood, and whether they affect males and females similarly is unknown. Here, we used chronic social defeat stress (CSDS) to induce depressive-like behaviors in male and female mice. Density of the mesolimbic and mesocortical projections was assessed via immuno-histochemistry combined with Sholl analysis along with the staining of activity-dependent markers pERK and c-fos in the ventral tegmental area (VTA), nucleus accumbens (NAc) and medial prefrontal cortex (mPFC). Our results show that social stress decreases the density of TH+ dopaminergic axonal projections in the deep layers of the mPFC in susceptible but not resilient male and female mice. Consistently, our analyses suggest that pERK expression is decreased in the mPFC but increased in the NAc following CSDS in males and females, with no change in c-fos expression in both sexes. Overall, our findings indicate that social defeat stress impacts the mesolimbic and mesocortical pathways by altering the molecular interactions regulating somatic and axonal plasticity in males and females.

Gene-environment interactions mediate stress susceptibility and resilience through the CaMKIIβ/TARPγ-8/AMPAR pathway

Although stressful events predispose individuals to psychiatric disorders, such as depression, not all people who undergo a stressful life experience become depressed, suggesting that gene-environment interactions (GxE) determine depression risk. The ventral hippocampus (vHPC) plays key roles in motivation, sociability, anhedonia, despair-like behaviors, anxiety, sleep, and feeding, pointing to the involvement of this brain region in depression. However, the molecular mechanisms underlying the cross talk between the vHPC and GxE in shaping behavioral susceptibility and resilience to chronic stress remain elusive. Here, we show that Ca2+/calmodulin-dependent protein kinase IIβ (CaMKIIβ) activity in the vHPC is differentially modulated in GxE mouse models of depression susceptibility and resilience, and that CaMKIIβ-mediated TARPγ-8 phosphorylation enhances the expression of AMPA receptor subunit GluA1 in the postsynaptic sites to enable stress resilience. We present previously missing molecular mechanisms underlying chronic stress-elicited behavioral changes, providing strategies for preventing and treating stress-related psychiatric disorders.

Transcriptome-wide association study identifies new susceptibility genes and pathways for depression

Depression is the most prevalent mental disorder with substantial morbidity and mortality. Although genome-wide association studies (GWASs) have identified multiple risk variants for depression, due to the complicated gene regulatory mechanisms and complexity of linkage disequilibrium (LD), the biological mechanisms by which the risk variants exert their effects on depression remain largely unknown. Here, we perform a transcriptome-wide association study (TWAS) of depression by integrating GWAS summary statistics from 807,553 individuals (246,363 depression cases and 561,190 controls) and summary-level gene-expression data (from the dorsolateral prefrontal cortex (DLPFC) of 1003 individuals). We identified 53 transcriptome-wide significant (TWS) risk genes for depression, of which 23 genes were not implicated in risk loci of the original GWAS. Seven out of 53 risk genes (B3GALTL, FADS1, TCTEX1D1, XPNPEP3, ZMAT2, ZNF501 and ZNF502) showed TWS associations with depression in two independent brain expression quantitative loci (eQTL) datasets, suggesting that these genes may represent promising candidates. We further conducted conditional analyses and identified the potential risk genes that driven the TWAS association signal in each locus. Finally, pathway enrichment analysis revealed biologically pathways relevant to depression. Our study identified new depression risk genes whose expression dysregulation may play a role in depression. More importantly, we translated the GWAS associations into risk genes and relevant pathways. Further mechanistic study and functional characterization of the TWS depression risk genes will facilitate the diagnostics and therapeutics for depression.

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.

Sex Selection Bias in Schizophrenia Antipsychotic Trials—An Update Systematic Review

The lack of female participation in antipsychotic trials for schizophrenia poses an important issue regarding its applicability, with direct and real-life repercussions to clinical practice. Here, our aim is to systematically review the sampling sex bias among randomized clinical trials (RCTs) of second-generation antipsychotics—namely risperidone, olanzapine, quetiapine, ziprasidone, and aripiprazole—as an update to a previous 2005 review. We searched MEDLINE and the Cochrane database for studies published through 7 September 2020 that assessed adult samples of at least 50 subjects with a diagnosis of schizophrenia, schizophrenia spectrum disorder, or broad psychosis, in order to investigate the percentage of women recruited and associated factors. Our review included 148 RCTs, published from 1993 to 2020, encompassing 43,961 subjects. Overall, the mean proportion of women was 34%, but only 17 trials included 50% or more females. Younger samples, studies conducted in North America, pharmaceutical funding and presence of specific exclusion criteria for women (i.e., pregnancy, breast-feeding or lack of reliable contraceptive) were associated with a lower prevalence of women in the trials. Considering the possible different effects of antipsychotics in both sexes, and our lack of knowledge on the subject due to sampling bias, it is imperative to expand actions aimed at bridging this gap.

Diagnostic Biomarker Hsa_circ_0126218 and Functioning Prediction in Peripheral Blood Monocular Cells of Female Patients With Major Depressive Disorder

Introduction

Although major depressive diroder (MDD) has brought huge burden and challenges to society globally, effective and accurate diagnoses and treatments remain inadequate. The pathogenesis that for women are more likely to suffer from depression than men needs to be excavated as well. The function of circRNAs in pathological process of depression has not been widely investigated. This study aims to explore potential diagnostic biomarker circRNA of female patients with MDD and to investigate its role in pathogenesis.

Methods

First, an expression profile of circRNAs in the peripheral blood monocular cells of MDD patients and healthy peripherals were established based on high-throughput sequencing analysis. In addition, the top 10 differentially expressed circRNAs were quantified by quantitative real-time PCR to explore diagnostic biomarkers. To further investigate the function of biomarkers in the pathogenesis of MDD, bioinformatics analysis on downstream target genes of the biomarkers was carried out.

Results

There is a mass of dysregulated circRNAs in PBMCs between female MDD patients and healthy controls. Among the top 10 differentially expressed circRNAs, hsa_circ_0126218 is more feasible as a diagnostic biomarker. The expression level of hsa_circ_0126218 displayed upregulation in patients with MDD and the area under the operating characteristic curve of hsa_circ_0126218 was 0.801 (95% CI 0.7226–0.8791, p < 0.0001). To explain the competing endogenous RNA role of hsa_circ_0126218 in the pathogenesis of female MDD, a hsa_circ_0126218-miRNA-mRNA network was established. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses stated that some of the enriched pathways downstream of hsa_circ_0126218 are closely related to MDD. Moreover, we established a protein-protein network to further screen out the hub genes (PIK3CA, PTEN, MAPK1, CDC42, Lyn, YES1, EPHB2, SMAD2, STAT1, and ILK). The function of hsa_circ_0126218 was refined by constructing a verified circRNA-predicted miRNA-hub gene subnetwork.

Conclusion

hsa_circ_0126218 can be considered as a new female MDD biomarker, and the pathogenesis of female MDD by the downstream regulation of hsa_circ_0126218 has been predicted. These findings may help further improve the early detection, effective diagnosis, convenient monitoring of complications, precise treatment, and timely recurrence prevention of depression.

Fate or coincidence: do COPD and major depression share genetic risk factors?

Major depressive disorder (MDD) is a common comorbidity in chronic obstructive pulmonary disease (COPD), affecting up to 57% of patients with COPD. Although the comorbidity of COPD and MDD is well established, the causal relationship between these two diseases is unclear. A large-scale electronic health record clinical biobank and genome-wide association study summary statistics for MDD and lung function traits were used to investigate potential shared underlying genetic susceptibility between COPD and MDD. Linkage disequilibrium score regression was used to estimate genetic correlation between phenotypes. Polygenic risk scores (PRS) for MDD and lung function traits were developed and used to perform a phenome-wide association study (PheWAS). Multi-trait-based conditional and joint analysis identified single-nucleotide polymorphisms (SNPs) influencing both lung function and MDD. We found genetic correlations between MDD and all lung function traits were small and not statistically significant. A PRS-MDD was significantly associated with an increased risk of COPD in a PheWAS [odds ratio (OR) = 1.12, 95% confidence interval (CI): 1.09-1.16] when adjusting for age, sex and genetic ancestry, but this relationship became attenuated when controlling for smoking history (OR = 1.08, 95% CI: 1.04-1.13). No significant associations were found between the lung function PRS and MDD. Multi-trait-based conditional and joint analysis identified three SNPs that may contribute to both traits, two of which were previously associated with mood disorders and COPD. Our findings suggest that the observed relationship between COPD and MDD may not be driven by a strong shared genetic architecture.

Long-term behavioral and cell-type-specific molecular effects of early life stress are mediated by H3K79me2 dynamics in medium spiny neurons

Animals susceptible to chronic social defeat stress (CSDS) exhibit depression-related behaviors, with aberrant transcription across several limbic brain regions, most notably in the nucleus accumbens (NAc). Early life stress (ELS) promotes susceptibility to CSDS in adulthood, but associated enduring changes in transcriptional control mechanisms in the NAc have not yet been investigated. In this study, we examined long-lasting changes to histone modifications in the NAc of male and female mice exposed to ELS. Dimethylation of lysine 79 of histone H3 (H3K79me2) and the enzymes (DOT1L and KDM2B) that control this modification are enriched in D2-type medium spiny neurons and are shown to be crucial for the expression of ELS-induced stress susceptibility. We mapped the site-specific regulation of this histone mark genome wide to reveal the transcriptional networks it modulates. Finally, systemic delivery of a small molecule inhibitor of DOT1L reversed ELS-induced behavioral deficits, indicating the clinical relevance of this epigenetic mechanism.

Regulation of depression-related behaviors by GABAergic neurons in the lateral septum through periaqueductal gray neuronal projections

Major depressive disorder (MDD) is a serious and widespread mental illness worldwide. The abnormality of neuronal networks may contribute to the etiology of MDD. However, the neural connections underlying the main symptoms of MDD need further elucidation. Here, we found that GABAergic neurons in the lateral septum (LS) were activated by chronic unpredictable stress (CUS), with increased numbers of ΔFosB-labeled neurons. LS neuronal activity was modulated using a chemogenetic approach. Activation of LS neurons caused a depressive phenotype, as shown by increased immobility in the forced swim test, and induced increased susceptibility to subthreshold chronic stress, as indicated by decreased female urine sniffing time and preference for sucrose in depression-related behavior detection, whereas suppression of LS neuronal activity induced an antidepressant effect under basal and stressed conditions. Moreover, we found that the LS showed strong neuronal projections to the dorsal periaqueductal gray (dPAG); activation of dPAG-projecting GABAergic neurons in the LS produced the same depressive behaviors and stress susceptibility as induced by the activation of the majority of LS GABAergic neurons. Finally, we found that activation of neuronal fibers in the dPAG derived from the LS showed depression-related behaviors, as suggested by the decreased female urine sniffing time and sucrose preference in female urine sniffing and sucrose preference tests respectively. Our findings indicate that LS is a key depression-controlling nucleus, and that the LS-PAG projection is an essential effector circuit for morbidity and treatment in depression.

Transcription Factor Motifs Associated with Anterior Insula Gene Expression Underlying Mood Disorder Phenotypes

Mood disorders represent a major cause of morbidity and mortality worldwide but the brain-related molecular pathophysiology in mood disorders remains largely undefined. Because the anterior insula is reduced in volume in patients with mood disorders, RNA was extracted from the anterior insula postmortem anterior insula of mood disorder samples and compared with unaffected controls for RNA-sequencing identification of differentially expressed genes (DEGs) in (a) bipolar disorder (BD; n = 37) versus (vs.) controls (n = 33), and (b) major depressive disorder (MDD n = 30) vs. controls, and (c) low vs. high axis I comorbidity (a measure of cumulative psychiatric disease burden). Given the regulatory role of transcription factors (TFs) in gene expression via specific-DNA-binding domains (motifs), we used JASPAR TF binding database to identify TF-motifs. We found that DEGs in BD vs. controls, MDD vs. controls, and high vs. low axis I comorbidity were associated with TF-motifs that are known to regulate expression of toll-like receptor genes, cellular homeostatic-control genes, and genes involved in embryonic, cellular/organ, and brain development. Robust imaging-guided transcriptomics by using meta-analytic imaging results to guide independent postmortem dissection for RNA-sequencing was applied by targeting the gray matter volume reduction in the anterior insula in mood disorders, to guide independent postmortem identification of TF motifs regulating DEG. Our findings of TF-motifs that regulate the expression of immune, cellular homeostatic-control, and developmental genes provide novel information about the hierarchical relationship between gene regulatory networks, the TFs that control them, and proximate underlying neuroanatomical phenotypes in mood disorders.

Chronic Ethanol Exposures Leads to a Negative Affective State in Female Rats That Is Accompanied by a Paradoxical Decrease in Ventral Hippocampus Excitability

Alcohol use disorder (AUD) differentially impacts men and women and a growing body of evidence points to sex-dependent adaptations in a number of brain regions. In a prior study, we explored the effect of a chronic intermittent ethanol exposure (CIE) model of AUD on neuronal and molecular adaptations in the dorsal and ventral domains of the hippocampus (dHC and vHC, respectively) in male rats. We found the vHC to be particularly sensitive to CIE, showing an increase in neuronal excitability and synaptic proteins associated with augmented excitation. These findings were accompanied by a CIE-dependent increase in anxiety-like behaviors. To explore sex-dependent adaptations in the hippocampus, we conducted a similar study in female rats. CIE-treated female rats showed a relatively modest increase in anxiety-like behaviors along with a robust increase in depressive-like measures. Despite both sexes showing clear evidence of a negative affective state following CIE, the vHC of females showed a decrease, rather than an increase, in neuronal excitability. In line with the reduced sensitivity to neural adaptations in the dHC of male rats, we were unable to identify any functional changes in the dHC of females. The functional changes of the vHC in female rats could not be explained by altered expression levels of a number of proteins typically associated with changes in neuronal excitability. Taken together, these findings point to sex as a major factor in CIE-dependent hippocampal adaptations that should be explored further to better understand possible gender differences in the etiology and treatment of AUD.

Genomic factors underlying sex differences in trauma-related disorders

Post-traumatic stress disorder (PTSD) is a devastating illness with treatment that is effective in only approximately half of the population. This limited rate of response highlights the necessity for research into underlying individual biological mechanisms that mediate development and progression of this disease, allowing for identification of patient-specific treatments. PTSD has clear sex differences in both risk and symptom patterns. Thus, one approach is to characterize trauma-related changes between men and women who exhibit differences in treatment efficacy and response to trauma. Recent technological advances in sequencing have identified several genomic loci and transcriptional changes that are associated with post-trauma symptomatology. However, although the diagnosis of PTSD is more prevalent in women, the genetic factors underlying sex differences remain poorly understood. Here, we review recent work that highlights current understanding and limitations in the field of sex differences in PTSD and related symptomatology.

Reduced anterior cingulate cortex volume induced by chronic stress correlates with increased behavioral emotionality and decreased synaptic puncta density

Clinical and preclinical studies report that chronic stress induces behavioral deficits as well as volumetric and synaptic alterations in corticolimbic brain regions including the anterior cingulate cortex (ACC), amygdala (AMY), nucleus accumbens (NAc) and hippocampus (HPC). Here, we aimed to investigate the volumetric changes associated with chronic restraint stress (CRS) and link these changes to the CRS-induced behavioral and synaptic deficits. We first confirmed that CRS increases behavioral emotionality, defined as collective scoring of anxiety- and anhedonia-like behaviors. We then demonstrated that CRS induced a reduction of total brain volume which negatively correlated with behavioral emotionality. Region-specific analysis identified that only the ACC showed significant decrease in volume following CRS (p < 0.05). Reduced ACC correlated with increased behavioral emotionality (r = -0.56; p = 0.0003). Although not significantly altered by CRS, AMY and NAc (but not the HPC) volumes were negatively correlated with behavioral emotionality. Finally, using structural covariance network analysis to assess shared volumetric variances between the corticolimbic brain regions and associated structures, we found a progressive decreased ACC degree and increased AMY degree following CRS. At the cellular level, reduced ACC volume correlated with decreased PSD95 (but not VGLUT1) puncta density (r = 0.35, p < 0.05), which also correlated with increased behavioral emotionality (r = -0.44, p < 0.01), suggesting that altered synaptic strength is an underlying substrate of CRS volumetric and behavioral effects. Our results demonstrate that CRS effects on ACC volume and synaptic density are linked to behavioral emotionality and highlight key ACC structural and morphological alterations relevant to stress-related illnesses including mood and anxiety disorders.

Alteration of lipids and amino acids in plasma distinguish schizophrenia patients from controls: A targeted metabolomics study

BACKGROUND

Schizophrenia (SCZ) is a serious psychiatric disorder. Metabolite disturbance is an important pathogenic factor in schizophrenic patients. In this study, we aim to identify plasma lipid and amino acid biomarkers for SCZ using targeted metabolomics.

METHODS

Plasma from 76 SCZ patients and 50 matched controls were analyzed using the LC/MS-based multiple reaction monitoring (MRM) metabolomics approach. A total of 182 targeted metabolites, including 22 amino acids and 160 lipids or lipid-related metabolites were observed. We used binary logistic regression analysis to determine whether the lipid and amino acid biomarkers could discriminate SCZ patients from controls. The area under the curve (AUC) from receiver operation characteristic (ROC) curve analysis was conducted to evaluate the diagnostic performance of the biomarkers panel.

RESULTS

We identified 19 significantly differentially expressed metabolites between the SCZ patients and the controls (false discovery rate < 0.05), including one amino acid and 18 lipids or lipid-related metabolites. The binary logistic regression-selected panel showed good diagnostic performance in the drug-naïve group (AUC = 0.936) and all SCZ patients (AUC = 0.948), especially in the drug-treated group (AUC = 0.963).

CONCLUSIONS

Plasma lipids and amino acids showed significant dysregulation in SCZ, which could effectively discriminate SCZ patients from controls. The LC/MS/MS-based approach provides reliable data for the objective diagnosis of SCZ.

Repeated morphine exposure activates synaptogenesis and other neuroplasticity-related gene networks in the dorsomedial prefrontal cortex of male and female rats

BACKGROUND

Opioid abuse is a chronic disorder likely involving stable neuroplastic modifications. While a number of molecules contributing to these changes have been identified, the broader spectrum of genes and gene networks that are affected by repeated opioid administration remain understudied.

METHODS

We employed Next-Generation RNA-sequencing (RNA-seq) followed by quantitative chromatin immunoprecipitation to investigate changes in gene expression and their regulation in adult male and female rats' dorsomedial prefrontal cortex (dmPFC) after a regimen of daily injection of morphine (5.0 mg/kg; 10 days). Ingenuity Pathway Analysis (IPA) was used to analyze affected molecular pathways, gene networks, and associated regulatory factors. A complementary behavioral study evaluated the effects of the same morphine injection regimen on locomotor activity, pain sensitivity, and somatic withdrawal signs.

RESULTS

Behaviorally, repeated morphine injection induced locomotor hyperactivity and hyperalgesia in both sexes. 90 % of differentially expressed genes (DEGs) in morphine-treated rats were upregulated in both males and females, with a 35 % overlap between sexes. A substantial number of DEGs play roles in synaptic signaling and neuroplasticity. Chromatin immunoprecipitation revealed enrichment of H3 acetylation, a transcriptionally activating chromatin mark. Although broadly similar, some differences were revealed in the gene ontology networks enriched in females and males.

CONCLUSIONS

Our results cohere with findings from previous studies based on a priori gene selection. Our results also reveal novel genes and molecular pathways that are upregulated by repeated morphine exposure, with some common to males and females and others that are sex-specific.

Adolescent stress sensitizes the adult neuroimmune transcriptome and leads to sex-specific microglial and behavioral phenotypes

Adolescent exposure to chronic stress, a risk factor for mood disorders in adulthood, sensitizes the neuroinflammatory response to a subsequent immune challenge. We previously showed that chronic adolescent stress (CAS) in rats led to distinct patterns of neuroimmune priming in adult male and female rats. However, sex differences in the neuroimmune consequences of CAS and their underlying mechanisms are not fully understood. Here we hypothesized that biological sex would dictate differential induction of inflammation-related transcriptomic pathways and immune cell involvement (microglia activation and leukocyte presence) in the hippocampus of male and female rats with a history of CAS. Adolescent rats underwent CAS (six restraint and six social defeat episodes during postnatal days 38-49), and behavioral assessments were conducted in adolescence and adulthood. Neuroimmune measures were obtained following vehicle or a systemic lipopolysaccharide (LPS) challenge in adulthood. CAS led to increased time in the corners of the open field in adolescence. In males, CAS also increased social avoidance. As adults, CAS rats displayed an exaggerated enrichment of the nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) pathway and chemokine induction following LPS challenge, and increased number of perivascular CD45⁺ cells in the hippocampus. However, CAS females, but not males, showed exaggerated glucocorticoid receptor (GR) pathway enrichment and increased microglial complexity. These results provide further insight to the mechanisms by which peripheral immune events may influence neuroimmune responses differentially among males and females and further demonstrate the importance of adolescent stress in shaping adult responses.

Dopamine and glutamate receptors control social stress-induced striatal ERK1/2 activation

Stress has been acknowledged as one of the main risk factors for the onset of psychiatric disorders. Social stress is the most common type of stressor encountered in our daily lives. Uncovering the molecular determinants of the effect of stress on the brain would help understanding the complex maladaptations that contribute to pathological stress-related mental states. We examined molecular changes in the reward system following social defeat stress in mice, as increasing evidence implicates this system in sensing stressful stimuli. Following acute or chronic social defeat stress, the activation (i.e. phosphorylation) of extracellular signal-regulated kinases ERK1 and ERK2 (pERK1/2), markers of synaptic plasticity, was monitored in sub-regions of the reward system. We employed pharmacological antagonists and inhibitory DREADD to dissect the sequence of events controlling pERK1/2 dynamics. The nucleus accumbens (NAc) showed marked increases in pERK1/2 following both acute and chronic social stress compared to the dorsal striatum. Increases in pERK1/2 required dopamine D1 receptors and GluN2B-containing NMDA receptors. Paraventricular thalamic glutamatergic inputs to the NAc are required for social stress-induced pERK1/2. The molecular adaptations identified here could contribute to the long-lasting impact of stress on the brain and may be targeted to counteract stress-related psychopathologies.

Brain-immune interactions in neuropsychiatric disorders: Lessons from transcriptome studies for molecular targeting

Understanding the pathophysiological mechanisms of neuropsychiatric disorders has been a challenging quest for neurobiologists. Recent years have witnessed enormous technological advances in the field of neuroimmunology, blurring boundaries between the central nervous system and the periphery. Consequently, the discipline has expanded to cover interactions between the nervous and immune systems in health and diseases. The complex interplay between the peripheral and central immune pathways in neuropsychiatric disorders has recently been documented in various studies, but the genetic determinants remain elusive. Recent transcriptome studies have identified dysregulated genes involved in peripheral immune cell activation, blood-brain barrier integrity, glial cell activation, and synaptic plasticity in major depressive disorder, bipolar disorder, autism spectrum disorder, and schizophrenia. Herein, the key transcriptomic techniques applied in investigating differentially expressed genes and pathways responsible for altered brain-immune interactions in neuropsychiatric disorders are discussed. The application of transcriptomics that can aid in identifying molecular targets in various neuropsychiatric disorders is highlighted.

Neural circuits and activity dynamics underlying sex-specific effects of chronic social isolation stress

Exposure to prolonged stress in critical developmental periods induces heightened vulnerability to psychiatric disorders, which may have sex-specific consequences. Here we investigate the neuronal circuits mediating behavioral changes in mice after chronic adolescent social isolation stress. Escalated aggression is exhibited in stressed males, while social withdrawal is shown in stressed females. In vivo multichannel recordings of free-moving animals indicate that pyramidal neurons in prefrontal cortex (PFC) from stressed males exhibit the significantly decreased spike activity during aggressive attacks, while PFC pyramidal neurons from stressed females show a blunted increase of discharge rates during sociability tests. Chemogenetic and electrophysiological evidence shows that PFC hypofunctioning and BLA principal neuron hyperactivity contribute to the elevated aggression in stressed males, while PFC hypofunctioning and VTA dopamine neuron hypoactivity contribute to the diminished sociability in stressed females. These results establish a framework for understanding the circuit and physiological mechanisms underlying sex-specific divergent effects of stress.

Mini-review: Elucidating the psychological, physical, and sex-based interactions between HIV infection and stress

Stress is generally classified as any mental or emotional strain resulting from difficult circumstances, and can manifest in the form of depression, anxiety, post-traumatic stress disorder (PTSD), or other neurocognitive disorders. Neurocognitive disorders such as depression, anxiety, and PTSD are large contributors to disability worldwide, and continue to affect individuals and communities. Although these disorders affect men and women, women are disproportionately represented among those diagnosed with affective disorders, a result of both societal gender roles and physical differences. Furthermore, the incidence of these neurocognitive disorders is augmented among People Living with HIV (PLWH); the physical ramifications of stress increase the likelihood of HIV acquisition, pathogenesis, and treatment, as both stress and HIV infection are characterized by chronic inflammation, which creates a more opportunistic environment for HIV. Although the stress response is facilitated by the autonomic nervous system (ANS) and the hypothalamic pituitary adrenal (HPA) axis, when the response involves a psychological component, additional brain regions are engaged. The impact of chronic stress exposure and the origin of individual variation in stress responses and resilience are at least in part attributable to regions outside the primary stress circuity, including the amygdala, prefrontal cortex, and hippocampus. This review aims to elucidate the relationship between stress and HIV, how these interact with sex, and to understand the physical ramifications of these interactions.

Depression treatment response to ketamine: sex-specific role of interleukin-8, but not other inflammatory markers

Inflammation plays a role in depression pathophysiology and treatment response, with effects varying by sex and therapeutic modality. Lower levels of interleukin(IL)-8 predict depression response to antidepressant medication and to electroconvulsive therapy (ECT), although ECT effects are specific to females. Whether IL-8 predicts depression response to ketamine and in a sex-specific manner is not known. Here, depressed patients (n = 46; female, n = 17) received open label infusion of ketamine (0.5 mg/kg over 40 min; NCT02165449). Plasma levels of IL-8 were evaluated at baseline and post-treatment. Baseline levels of IL-8 had a trending association with response to ketamine, depending upon sex (responder status × sex interaction: p = 0.096), in which lower baseline levels of IL-8 in females (p = 0.095) but not males (p = 0.96) trended with treatment response. Change in levels of IL-8 from baseline to post-treatment differed significantly by responder status (defined as ≥50% reduction in Hamilton Depression Rating Scale [HAM-D] Score), depending upon sex (responder status × sex × time interaction: F(1,42)=6.68, p = 0.01). In addition, change in IL-8 interacted with sex to predict change in HAM-D score (β = -0.63, p = 0.003); increasing IL-8 was associated with decreasing HAM-D score in females (p = 0.08) whereas the inverse was found in males (p = 0.02). Other inflammatory markers (IL-6, IL-10, tumor necrosis factor-α, C-reactive protein) were explored with no significant relationships identified. Given these preliminary findings, further evaluation of sex differences in the relationship between IL-8 and treatment response is warranted to elucidate mechanisms of response and aid in the development of personalized approaches to depression treatment.

Sex-differential DNA methylation and associated regulation networks in human brain implicated in the sex-biased risks of psychiatric disorders

Many psychiatric disorders are characterized by a strong sex difference, but the mechanisms behind sex-bias are not fully understood. DNA methylation plays important roles in regulating gene expression, ultimately impacting sexually different characteristics of the human brain. Most previous literature focused on DNA methylation alone without considering the regulatory network and its contribution to sex-bias of psychiatric disorders. Since DNA methylation acts in a complex regulatory network to connect genetic and environmental factors with high-order brain functions, we investigated the regulatory networks associated with different DNA methylation and assessed their contribution to the risks of psychiatric disorders. We compiled data from 1408 postmortem brain samples in 3 collections to identify sex-differentially methylated positions (DMPs) and regions (DMRs). We identified and replicated thousands of DMPs and DMRs. The DMR genes were enriched in neuronal related pathways. We extended the regulatory networks related to sex-differential methylation and psychiatric disorders by integrating methylation quantitative trait loci (meQTLs), gene expression, and protein-protein interaction data. We observed significant enrichment of sex-associated genes in psychiatric disorder-associated gene sets. We prioritized 2080 genes that were sex-biased and associated with psychiatric disorders, such as NRXN1, NRXN2, NRXN3, FDE4A, and SHANK2. These genes are enriched in synapse-related pathways and signaling pathways, suggesting that sex-differential genes of these neuronal pathways may cause the sex-bias of psychiatric disorders.

Hepatic Molecular Signatures Highlight the Sexual Dimorphism of Nonalcoholic Steatohepatitis (NASH)

BACKGROUND AND AIMS

Nonalcoholic steatohepatitis (NASH) is considered as a pivotal stage in nonalcoholic fatty liver disease (NAFLD) progression, given that it paves the way for severe liver injuries such as fibrosis and cirrhosis. The etiology of human NASH is multifactorial, and identifying reliable molecular players and/or biomarkers has proven difficult. Together with the inappropriate consideration of risk factors revealed by epidemiological studies (altered glucose homeostasis, obesity, ethnicity, sex, etc.), the limited availability of representative NASH cohorts with associated liver biopsies, the gold standard for NASH diagnosis, probably explains the poor overlap between published "omics"-defined NASH signatures.

APPROACH AND RESULTS

Here, we have explored transcriptomic profiles of livers starting from a 910-obese-patient cohort, which was further stratified based on stringent histological characterization, to define "NoNASH" and "NASH" patients. Sex was identified as the main factor for data heterogeneity in this cohort. Using powerful bootstrapping and random forest (RF) approaches, we identified reliably differentially expressed genes participating in distinct biological processes in NASH as a function of sex. RF-calculated gene signatures identified NASH patients in independent cohorts with high accuracy.

CONCLUSIONS

This large-scale analysis of transcriptomic profiles from human livers emphasized the sexually dimorphic nature of NASH and its link with fibrosis, calling for the integration of sex as a major determinant of liver responses to NASH progression and responses to drugs.

Transcriptional markers of excitation-inhibition balance in germ-free mice show region-specific dysregulation and rescue after bacterial colonization

BACKGROUND

Studies of germ-free (GF) mice demonstrate that gut microbiota can influence behaviour by modulating neurochemical pathways in the brain, and that bacterial colonization normalizes behavioural deficits in GF-mice. Since disrupted GABAergic and glutamatergic signaling are reported in mood disorders, this study investigated the effect of gut microbiota manipulations on EIB-relevant gene expression in the brain.

METHODS

GF Swiss-Webster mice were colonized with E. coli JM83, complex microbiota (specific-pathogen-free; SPF), or no microbiota, and compared with controls (n = 6/group). 21 synaptic genes representing GABAergic, glutamatergic, BDNF, and astrocytic functions were measured in the hippocampus, amygdala, and prefrontal cortex using quantitative PCR. Gene co-expression analysis was used to identify gene modules related to colonization status, and compared by permutation analysis. Gene expression profiles were compared to existing post-mortem cohorts of depressed subjects (n = 28 cases vs 28 controls).

RESULTS

Region-specific alterations in gene expression were observed in GF-mice compared to controls. 58% of all genes (14/24) altered in GF-mice were normalized following SPF-colonization. GF-mice displayed disorganization of gene co-expression networks in all three brain regions (hippocampus, p = 0.0003; amygdala, p = 0.0012; mPFC, p = 0.0069), which was restored by SPF colonization in hippocampus (p v.s. GF = 0.0003, p v.s. control = 0.60). The hippocampal gene expression profile in GF-mice was significantly correlated with that in human depression (ρ = 0.51, p = 0.027), and this correlation was not observed after colonization.

CONCLUSION

Together, we show that the absence of gut microbiota disrupts the expression of EIB-relevant genes in mice, and colonization restores EIB-relevant expression, in ways that are relevant to human depression.

Experience and activity-dependent control of glucocorticoid receptors during the stress response in large-scale brain networks

The diversity of actions of the glucocorticoid stress hormones among individuals and within organs, tissues and cells is shaped by age, gender, genetics, metabolism, and the quantity of exposure. However, such factors cannot explain the heterogeneity of responses in the brain within cells of the same lineage, or similar tissue environment, or in the same individual. Here, we argue that the stress response is continuously updated by synchronized neural activity on large-scale brain networks. This occurs at the molecular, cellular and behavioral levels by crosstalk communication between activity-dependent and glucocorticoid signaling pathways, which updates the diversity of responses based on prior experience. Such a Bayesian process determines adaptation to the demands of the body and external world. We propose a framework for understanding how the diversity of glucocorticoid actions throughout brain networks is essential for supporting optimal health, while its disruption may contribute to the pathophysiology of stress-related disorders, such as major depression, and resistance to therapeutic treatments.

Sex-Specific Role for SLIT1 in Regulating Stress Susceptibility

BACKGROUND

Major depressive disorder is a pervasive and debilitating syndrome characterized by mood disturbances, anhedonia, and alterations in cognition. While the prevalence of major depressive disorder is twice as high for women as men, little is known about the molecular mechanisms that drive sex differences in depression susceptibility.

METHODS

We discovered that SLIT1, a secreted protein essential for axonal navigation and molecular guidance during development, is downregulated in the adult ventromedial prefrontal cortex (vmPFC) of women with depression compared with healthy control subjects, but not in men with depression. This sex-specific downregulation of Slit1 was also observed in the vmPFC of mice exposed to chronic variable stress. To identify a causal, sex-specific role for SLIT1 in depression-related behavioral abnormalities, we performed knockdown (KD) of Slit1 expression in the vmPFC of male and female mice.

RESULTS

When combined with stress exposure, vmPFC Slit1 KD reflected the human condition by inducing a sex-specific increase in anxiety- and depression-related behaviors. Furthermore, we found that vmPFC Slit1 KD decreased the dendritic arborization of vmPFC pyramidal neurons and decreased the excitability of the neurons in female mice, effects not observed in males. RNA sequencing analysis of the vmPFC after Slit1 KD in female mice revealed an augmented transcriptional stress signature.

CONCLUSIONS

Together, our findings establish a crucial role for SLIT1 in regulating neurophysiological and transcriptional responses to stress within the female vmPFC and provide mechanistic insight into novel signaling pathways and molecular factors influencing sex differences in depression susceptibility.

Sex-Specific Transcriptional Changes in Response to Adolescent Social Stress in the Brain's Reward Circuitry

BACKGROUND

Sex differences in addiction have been described in humans and animal models. A key factor that influences addiction in both males and females is adolescent experience. Adolescence is associated with higher vulnerability to substance use disorders, and male rodents subjected to adolescent social isolation (SI) stress form stronger preferences for drugs of abuse in adulthood. However, little is known about how females respond to SI, and few studies have investigated the transcriptional changes induced by SI in the brain's reward circuitry.

METHODS

We tested the hypothesis that SI alters the transcriptome in a persistent and sex-specific manner in prefrontal cortex, nucleus accumbens, and ventral tegmental area. Mice were isolated or group housed from postnatal day P22 to P42, then group housed until ∼P90. Transcriptome-wide changes were investigated by RNA sequencing after acute or chronic cocaine or saline administration.

RESULTS

We found that SI disrupts sex-specific transcriptional responses to cocaine and reduces sex differences in gene expression across all three brain regions. Furthermore, SI induces gene expression profiles in males that more closely resemble group-housed females, suggesting that SI "feminizes" the male transcriptome. Coexpression analysis reveals that such disruption of sex differences in gene expression alters sex-specific gene networks and identifies potential sex-specific key drivers of these transcriptional changes.

CONCLUSIONS

Together, these data show that SI has region-specific effects on sex-specific transcriptional responses to cocaine and provide a better understanding of reward-associated transcription that differs in males and females.

Transcriptomic analyses of humans and mice provide insights into depression

Accumulating studies have been conducted to identify risk genes and relevant biological mechanisms underlying major depressive disorder (MDD). In particular, transcriptomic analyses in brain regions engaged in cognitive and emotional processes, e.g., the dorsolateral prefrontal cortex (DLPFC), have provided essential insights. Based on three independent DLPFC RNA-seq datasets of 79 MDD patients and 75 healthy controls, we performed differential expression analyses using two alternative approaches for cross-validation. We also conducted transcriptomic analyses in mice undergoing chronic variable stress (CVS) and chronic social defeat stress (CSDS). We identified 12 differentially expressed genes (DEGs) through both analytical methods in MDD patients, the majority of which were also dysregulated in stressed mice. Notably, the mRNA level of the immediate early gene FOS ( Fos proto-oncogene) was significantly decreased in both MDD patients and CVS-exposed mice, and CSDS-susceptible mice exhibited a greater reduction in Fos expression compared to resilient mice. These findings suggest the potential key roles of this gene in the pathogenesis of MDD related to stress exposure. Altered transcriptomes in the DLPFC of MDD patients might be, at least partially, the result of stress exposure, supporting that stress is a primary risk factor for MDD.

Creation of a gene expression portrait of depression and its application for identifying potential treatments

Depression is a complex mental health disorder and the goal here was to identify a consistent underlying portrait of expression that ranks all genes from most to least dysregulated and indicates direction of change relative to controls. Using large-scale neural gene expression depression datasets, a combined portrait (for men and women) was created along with one for men and one for women only. The depressed brain was characterized by a "hypo" state, that included downregulation of activity-related genes, including EGR1, FOS, and ARC, and indications of a lower brain temperature and sleep-like state. MAP kinase and BDNF pathways were enriched with overlapping genes. Expression patterns suggested decreased signaling for GABA and for neuropeptides, CRH, SST, and CCK. GWAS depression genes were among depression portrait genes and common genes of interest included SPRY2 and PSEN2. The portraits were used with the drug repurposing approach of signature matching to identify treatments that could reverse depression gene expression patterns. Exercise was identified as the top treatment for depression for the combined and male portraits. Other non-traditional treatments that scored well were: curcumin, creatine, and albiflorin. Fluoxetine scored best among typical antidepressants. The creation of the portraits of depression provides new insights into the complex landscape of depression and a novel platform for evaluating and identifying potential new treatments.