Genetics and Brain Transcriptomics of Completed Suicide

Omics Approaches to Investigate the Pathogenesis of Suicide

Suicide is the second leading cause of death in U.S. adolescents and young adults and is generally associated with a psychiatric disorder. Suicidal behavior has a complex etiology and pathogenesis. Moderate heritability suggests genetic causes. Associations between childhood and recent life adversity indicate contributions from epigenetic factors. Genomic contributions to suicide pathogenesis remain largely unknown. This article is based on a workshop held to design strategies to identify molecular drivers of suicide neurobiology that would be putative new treatment targets. The panel determined that while bulk tissue studies provide comprehensive information, single-nucleus approaches that identify cell type-specific changes are needed. While single-nuclei techniques lack information on cytoplasm, processes, spines, and synapses, spatial multiomic technologies on intact tissue detect cell alterations specific to brain tissue layers and subregions. Because suicide has genetic and environmental drivers, multiomic approaches that combine cell type-specific epigenome, transcriptome, and proteome provide a more complete picture of pathogenesis. To determine the direction of effect of suicide risk gene variants on RNA and protein expression and how these interact with epigenetic marks, single-nuclei and spatial multiomics quantitative trait loci maps should be integrated with whole-genome sequencing and genome-wide association databases. The workshop concluded with a recommendation for the formation of an international suicide biology consortium that will bring together brain banks and investigators with expertise in cutting-edge omics technologies to delineate the biology of suicide and identify novel potential treatment targets to be tested in cellular and animal models for drug and biomarker discovery to guide suicide prevention.

Altered transcriptomes, cell type proportions, and dendritic spine morphology in hippocampus of suicide decedents

BACKGROUND

Suicide is a manner of death resulting from complex environmental and genetic risks that affect millions of people globally. Both structural and functional studies identified the hippocampus as one of the vulnerable brain regions contributing to suicide risk.

METHODS

We have identified the hippocampal tissue transcriptomes, gene ontology, cell type proportions, and dendritic spine morphology in controls (n = 28) and suicide decedents (n = 22). In addition, the transcriptomic signature in iPSC-derived neuronal precursor cells (NPCs) and neurons were also investigated in controls (n = 2) and suicide decedents (n = 2).

RESULTS

The hippocampal tissue transcriptomic data revealed that NPAS4 gene expression was downregulated while ALDH1A2, NAAA, and MLXIPL gene expressions were upregulated in hippocampal tissue of suicide decedents. The gene ontology identified 29 significant pathways including NPAS4-associated gene ontology terms "excitatory post-synaptic potential", "regulation of postsynaptic membrane potential" and "long-term memory" indicating alteration of glutamatergic synapses in the hippocampus of suicide decedents. The cell type deconvolution identified decreased excitatory neuron proportion and an increased inhibitory neuron proportion providing evidence of excitation/inhibition imbalance in the hippocampus of suicide decedents. In addition, suicide decedents had increased dendric spine density in the hippocampus, due to an increase of thin (relatively unstable) dendritic spines, compared to controls. The transcriptomes of iPSC-derived hippocampal-like NPCs and neurons revealed 31 and 33 differentially expressed genes in NPC and neurons, respectively, of suicide decedents.

CONCLUSIONS

Our findings will provide new insights into the hippocampal neuropathology of suicide.

Reverse phase protein array-based investigation of mitochondrial genes reveals alteration of glutaminolysis in the parahippocampal cortex of people who died by suicide

A moderating hub between resting state networks (RSNs) and the medial temporal lobe (MTL) is the parahippocampal cortex (PHC). Abnormal activity has been reported in depressed patients and suicide attempters in this region. Alterations in neuronal mitochondrial function may contribute to depression and suicidal behavior. However, little is known about the underlying molecular level changes in relevant structures. Specifically, expressional changes related to suicide have not been reported in the PHC. In this study, we compared the protein expression levels of genes encoding tricarboxylic acid (TCA) cycle enzymes in the PHC of adult individuals who died by suicide by reverse phase protein array (RPPA), which was corroborated by qRT-PCR at the mRNA level. Postmortem human brain samples were collected from 12 control and 10 suicidal individuals. The entorhinal cortex, which is topographically anterior to the PHC in the parahippocampal gyrus, and some other cortical brain regions were utilized for comparison. The results of the RPPA analysis revealed that the protein levels of DLD, OGDH, SDHB, SUCLA2, and SUCLG2 subunits were significantly elevated in the PHC but not in other cortical brain regions. In accordance with these findings, the mRNA levels of the respective subunits were also increased in the PHC. The subunits with altered levels are implicated in enzyme complexes involved in the oxidative decarboxylation branch of glutamine catabolism. These data suggest a potential role of glutaminolysis in the pathophysiology of suicidal behavior in the PHC.

Associations of the immune system in aggression traits and the role of microglia as mediators

There is an important relationship between the immune system and aggressive behavior. Aggressive encounters acutely increase the levels of proinflammatory cytokines, and there are positive correlations between aggressive traits and peripheral proinflammatory cytokines. Endotoxin lipopolysaccharide (LPS) treatment, which results in peripheral immune activation, decreases aggressive behavior as one of the sickness behavioral symptoms. In contrast, certain brain infections and chronic interferon treatment are associated with increased aggression. Indeed, the effects of proinflammatory cytokines on the brain in aggressive behavior are bidirectional, depending on the type and dose of cytokine, target brain region, and type of aggression. Some studies have suggested that microglial activation and neuroinflammation influence intermale aggression in rodent models. In addition, pathological conditions as well as physiological levels of cytokines produced by microglia play an important role in social and aggressive behavior in adult animals. Furthermore, microglial function in early development is necessary for the establishment of the social brain and the expression of juvenile social behaviors, including play fighting. Overall, this review discusses the important link between the immune system and aggressive traits and the role of microglia as mediators of this link.

Prenatal opioid exposure significantly impacts placental protein kinase C (PKC) and drug transporters, leading to drug resistance and neonatal opioid withdrawal syndrome

Background

Neonatal Opioid Withdrawal Syndrome (NOWS) is a consequence of in-utero exposure to prenatal maternal opioids, resulting in the manifestation of symptoms like irritability, feeding problems, tremors, and withdrawal signs. Opioid use disorder (OUD) during pregnancy can profoundly impact both mother and fetus, disrupting fetal brain neurotransmission and potentially leading to long-term neurological, behavioral, and vision issues, and increased infant mortality. Drug resistance complicates OUD and NOWS treatment, with protein kinase regulation of drug transporters not fully understood.

Methods

DNA methylation levels of ATP-binding cassette (ABC) and solute carrier (SLC) drug transporters, along with protein kinase C (PKC) genes, were assessed in 96 placental samples using the Illumina Infinium MethylationEPIC array (850K). Samples were collected from three distinct groups: 32 mothers with infants prenatally exposed to opioids who needed pharmacological intervention for NOWS, 32 mothers with prenatally opioid-exposed infants who did not necessitate NOWS treatment, and 32 mothers who were not exposed to opioids during pregnancy.

Results

We identified 69 significantly differentially methylated SLCs, with 24 hypermethylated and 34 hypomethylated, and 11 exhibiting both types of methylation changes including SLC13A3, SLC15A2, SLC16A11, SLC16A3, SLC19A2, and SLC26A1. We identified methylation changes in 11 ABC drug transporters (ABCA1, ABCA12, ABCA2, ABCB10, ABCB5, ABCC12, ABCC2, ABCC9, ABCE1, ABCC7, ABCB3): 3 showed hypermethylation, 3 hypomethylation, and 5 exhibited both. Additionally, 7 PKC family genes (PRKCQ, PRKAA1, PRKCA, PRKCB, PRKCH, PRKCI, and PRKCZ) showed methylation changes. These genes are associated with 13 pathways involved in NOWS, including ABC transporters, bile secretion, pancreatic secretion, insulin resistance, glutamatergic synapse, and gastric acid secretion.

Conclusion

We report epigenetic changes in PKC-related regulation of drug transporters, which could improve our understanding of clinical outcomes like drug resistance, pharmacokinetics, drug-drug interactions, and drug toxicity, leading to maternal relapse and severe NOWS. Novel drugs targeting PKC pathways and transporters may improve treatment outcomes for OUD in pregnancy and NOWS.

Uncommon Protein-Coding Variants Associated With Suicide Attempt in a Diverse Sample of U.S. Army Soldiers

BACKGROUND

Suicide is a societal and public health concern of global scale. Identifying genetic risk factors for suicide attempt can characterize underlying biology and enable early interventions to prevent deaths. Recent studies have described common genetic variants for suicide-related behaviors. Here, we advance this search for genetic risk by analyzing the association between suicide attempt and uncommon variation exome-wide in a large, ancestrally diverse sample.

METHODS

We sequenced whole genomes of 13,584 soldiers from the Army STARRS (Army Study to Assess Risk and Resilience in Servicemembers), including 979 individuals with a history of suicide attempt. Uncommon, nonsilent protein-coding variants were analyzed exome-wide for association with suicide attempt using gene-collapsed and single-variant analyses.

RESULTS

We identified 19 genes with variants enriched in individuals with history of suicide attempt, either through gene-collapsed or single-variant analysis (Bonferroni padjusted < .05). These genes were CIB2, MLF1, HERC1, YWHAE, RCN2, VWA5B1, ATAD3A, NACA, EP400, ZNF585A, LYST, RC3H2, PSD3, STARD9, SGMS1, ACTR6, RGS7BP, DIRAS2, and KRTAP10-1. Most genes had variants across multiple genomic ancestry groups. Seventeen of these genes were expressed in healthy brain tissue, with 9 genes expressed at the highest levels in the brain versus other tissues. Brains from individuals deceased from suicide aberrantly expressed RGS7BP (padjusted = .035) in addition to nominally significant genes including YWHAE and ACTR6, all of which have reported associations with other mental disorders.

CONCLUSIONS

These results advance the molecular characterization of suicide attempt behavior and support the utility of whole-genome sequencing for complementing the findings of genome-wide association studies in suicide research.

Alcohol use disorder and risk of specific methods of suicide death in a national cohort

INTRODUCTION

Alcohol use disorder (AUD) is among the strongest correlates of suicide death, but it is unclear whether AUD status is differentially associated with risk of suicide by particular methods.

METHODS

The authors used competing risks models to evaluate the association between AUD status and risk of suicide by poisoning, suffocation, drowning, firearm, instruments, jumping, or other means in a large Swedish cohort born 1932-1995 (total N = 6,581,827; 48.8% female). Data were derived from Swedish national registers, including the Cause of Death Register and a range of medical registers.

RESULTS

After adjusting for sociodemographic factors and familial liability to suicidal behavior, AUD was positively associated with risk of suicide for each method evaluated (cumulative incidence differences: 0.006-1.040 for females, 0.046-0.680 for males), except the association with firearm suicide in females. AUD was most strongly associated with risk of suicide by poisoning. Sex differences in the effects of AUD and family liability were observed for some, but not all, methods. Furthermore, high familial liability for suicidal behavior exacerbated AUD's impact on risk for suicide by poisoning (both sexes) and suffocation and jumping (males only), while the inverse interaction was observed for firearm suicide (males only).

CONCLUSIONS

AUD increases risk of suicide by all methods examined and is particularly potent with respect to risk of suicide by poisoning. Differences in risk related to sex and familial liability to suicidal behavior underscore AUD's nuanced role in suicide risk. Future research should investigate targeted means restriction effectiveness among persons with AUD.

Glial Markers of Suicidal Behavior in the Human Brain-A Systematic Review of Postmortem Studies

Suicide is a major public health priority, and its molecular mechanisms appear to be related to glial abnormalities and specific transcriptional changes. This study aimed to identify and synthesize evidence of the relationship between glial dysfunction and suicidal behavior to understand the neurobiology of suicide. As of 26 January 2024, 46 articles that met the inclusion criteria were identified by searching PubMed and ISI Web of Science. Most postmortem studies, including 30 brain regions, have determined no density or number of total Nissl-glial cell changes in suicidal patients with major psychiatric disorders. There were 17 astrocytic, 14 microglial, and 9 oligodendroglial studies using specific markers of each glial cell and further on their specific gene expression. Those studies suggest that astrocytic and oligodendroglial cells lost but activated microglia in suicides with affective disorder, bipolar disorders, major depression disorders, or schizophrenia in comparison with non-suicided patients and non-psychiatric controls. Although the data from previous studies remain complex and cannot fully explain the effects of glial cell dysfunction related to suicidal behaviors, they provide risk directions potentially leading to suicide prevention.

Homicide or Happiness: Did Folate Fortification and Public Health Campaigns Influence Homicide Rates and the Great American Crime Decline?

The last several years have witnessed a remarkable growth in research directed at nutrition and behavior, with increased interest in the field of nutritional criminology. It is becoming clear that dietary patterns and specific nutrients play an important role in cognition and behavior, including those related to aggression, violence, and antisocial activity. Included in this expanding knowledge base is the recognition that folate, through multiple pathways, including enzymatic reactions and gut microbiome ecology, plays a critical role in central nervous system functioning. These mechanistic advances allow for a retrospective analysis of a topic that remains unexplained-the sudden and unpredicted drop in homicide and other violent crime rates in the United States and other nations in the 1990s. Here, we revisit this marked reduction in homicide rates through the lens of the coincident public health campaign (and subsequent mandatory fortification) to increase folic acid intake. Based on objectively measured blood folate levels through the National Health and Nutrition Examination Surveys, there is little doubt that tissue folate witnessed a dramatic rise at the national level from 1988 through 2000. Drawing from accumulated and emerging research on the neurobehavioral aspects of folate, it is our contention that this relatively sudden and massive increase in tissue folate levels may have contributed to reductions in violent crime in the United States.

Depicting the molecular features of suicidal behavior: a review from an "omics" perspective

Background Suicide is one of the leading global causes of death. Behavior patterns from suicide ideation to completion are complex, involving multiple risk factors. Advances in technologies and large-scale bioinformatic tools are changing how we approach biomedical problems. The "omics" field may provide new knowledge about suicidal behavior to improve identification of relevant biological pathways associated with suicidal behavior. Methods We reviewed transcriptomic, proteomic, and metabolomic studies conducted in blood and post-mortem brains from individuals who experienced suicide or suicidal behavior. Omics data were combined using systems biology in silico, aiming at identifying major biological mechanisms and key molecules associated with suicide. Results Post-mortem samples of suicide completers indicate major dysregulations in pathways associated with glial cells (astrocytes and microglia), neurotransmission (GABAergic and glutamatergic systems), neuroplasticity and cell survivor, immune responses and energy homeostasis. In the periphery, studies found alterations in molecules involved in immune responses, polyamines, lipid transport, energy homeostasis, and amino and nucleic acid metabolism. Limitations We included only exploratory, non-hypothesis-driven studies; most studies only included one brain region and whole tissue analysis, and focused on suicide completers who were white males with almost none confounding factors. Conclusions We can highlight the importance of synaptic function, especially the balance between the inhibitory and excitatory synapses, and mechanisms associated with neuroplasticity, common pathways associated with psychiatric disorders. However, some of the pathways highlighted in this review, such as transcriptional factors associated with RNA splicing, formation of cortical connections, and gliogenesis, point to mechanisms that still need to be explored.

Impact of Toxoplasma gondii and Human Microbiome on Suicidal Behavior: A Systematic Review

BACKGROUND

Suicide remains a persistent global health challenge, resisting widespread prevention efforts. According to previous findings, toxoplasmosis is particularly associated with altered decision making, which could lead to risk-taking behavior, thereby increasing the likelihood for suicidal behavior (SB). In addition, discussion about the role of microbiome in psychiatric disorders has emerged lately, which also makes it relevant to investigate its role in the context of SB. Therefore, two systematic reviews are integrated in this paper, and the existing knowledge is comprehensively summarized regarding the association between microbial pathogens and SB.

METHODS

We conducted a systematic search with keywords including SB and Toxoplasma gondii (Suicid* AND Toxoplasm*) and microbiome (Suicid* AND Microbiome AND Microbiota) throughout PubMed and Scopus to retrieve related studies up to 9 November 2023, identifying 24 eligible records. The subjects of the included studies had to have fulfilled the criteria of an SB disorder as defined by DSM-5, and death cases needed to have been defined as suicide.

RESULTS

Most studies reported significant association between toxoplasmosis and SB, suggesting a higher likelihood of SB in the infected population. Regarding the microbiome, only very few studies investigated an association between SB and alterations in the microbiome. Based on six included studies, there were some indications of a link between changes in the microbiome and SB.

CONCLUSION

The cognitive aspects of decision making in T. gondii-infected individuals with SB should be further investigated to unravel the underlying mechanisms. Further sufficiently powered studies are needed to establish a link between SB and alterations in the microbiome.

Integrative transcriptome- and DNA methylation analysis of brain tissue from the temporal pole in suicide decedents and their controls

Suicide rates have increased steadily world-wide over the past two decades, constituting a serious public health crisis that creates a significant burden to affected families and the society as a whole. Suicidal behavior involves a multi-factorial etiology, including psychological, social and biological factors. Since the molecular neural mechanisms of suicide remain vastly uncharacterized, we examined transcriptional- and methylation profiles of postmortem brain tissue from subjects who died from suicide as well as their neurotypical healthy controls. We analyzed temporal pole tissue from 61 subjects, largely free from antidepressant and antipsychotic medication, using RNA-sequencing and DNA-methylation profiling using an array that targets over 850,000 CpG sites. Expression of NPAS4, a key regulator of inflammation and neuroprotection, was significantly downregulated in the suicide decedent group. Moreover, we identified a total of 40 differentially methylated regions in the suicide decedent group, mapping to seven genes with inflammatory function. There was a significant association between NPAS4 DNA methylation and NPAS4 expression in the control group that was absent in the suicide decedent group, confirming its dysregulation. NPAS4 expression was significantly associated with the expression of multiple inflammatory factors in the brain tissue. Overall, gene sets and pathways closely linked to inflammation were significantly upregulated, while specific pathways linked to neuronal development were suppressed in the suicide decedent group. Excitotoxicity as well as suppressed oligodendrocyte function were also implicated in the suicide decedents. In summary, we have identified central nervous system inflammatory mechanisms that may be active during suicidal behavior, along with oligodendrocyte dysfunction and altered glutamate neurotransmission. In these processes, NPAS4 might be a master regulator, warranting further studies to validate its role as a potential biomarker or therapeutic target in suicidality.

Integrative Analyses of scRNA-seq, Bulk mRNA-seq, and DNA Methylation Profiling in Depressed Suicide Brain Tissues

BACKGROUND

Suicidal behaviors have become a serious public health concern globally due to the economic and human cost of suicidal behavior to individuals, families, communities, and society. However, the underlying etiology and biological mechanism of suicidal behavior remains poorly understood.

METHODS

We collected different single omic data, including single-cell RNA sequencing (scRNA-seq), bulk mRNA-seq, DNA methylation microarrays from the cortex of Major Depressive Disorder (MDD) in suicide subjects' studies, as well as fluoxetine-treated rats brains. We matched subject IDs that overlapped between the transcriptome dataset and the methylation dataset. The differential expression genes and differentially methylated regions were calculated with a 2-group comparison analysis. Cross-omics analysis was performed to calculate the correlation between the methylated and transcript levels of differentially methylated CpG sites and mapped transcripts. Additionally, we performed a deconvolution analysis for bulk mRNA-seq and DNA methylation profiling with scRNA-seq as the reference profiles.

RESULTS

Difference in cell type proportions among 7 cell types. Meanwhile, our analysis of single-cell sequence from the antidepressant-treated rats found that drug-specific differential expression genes were enriched into biological pathways, including ion channels and glutamatergic receptors.

CONCLUSIONS

This study identified some important dysregulated genes influenced by DNA methylation in 2 brain regions of depression and suicide patients. Interestingly, we found that oligodendrocyte precursor cells (OPCs) have the most contributors for cell-type proportions related to differential expression genes and methylated sites in suicidal behavior.

Metabolic features of treatment-refractory major depressive disorder with suicidal ideation

Peripheral blood metabolomics was used to gain chemical insight into the biology of treatment-refractory Major Depressive Disorder with suicidal ideation, and to identify individualized differences for personalized care. The study cohort consisted of 99 patients with treatment-refractory major depressive disorder and suicidal ideation (trMDD-SI n = 52 females and 47 males) and 94 age- and sex-matched healthy controls (n = 48 females and 46 males). The median age was 29 years (IQR 22-42). Targeted, broad-spectrum metabolomics measured 448 metabolites. Fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15) were measured as biomarkers of mitochondrial dysfunction. The diagnostic accuracy of plasma metabolomics was over 90% (95%CI: 0.80-1.0) by area under the receiver operator characteristic (AUROC) curve analysis. Over 55% of the metabolic impact in males and 75% in females came from abnormalities in lipids. Modified purines and pyrimidines from tRNA, rRNA, and mRNA turnover were increased in the trMDD-SI group. FGF21 was increased in both males and females. Increased lactate, glutamate, and saccharopine, and decreased cystine provided evidence of reductive stress. Seventy-five percent of the metabolomic abnormalities found were individualized. Personalized deficiencies in CoQ10, flavin adenine dinucleotide (FAD), citrulline, lutein, carnitine, or folate were found. Pathways regulated by mitochondrial function dominated the metabolic signature. Peripheral blood metabolomics identified mitochondrial dysfunction and reductive stress as common denominators in suicidal ideation associated with treatment-refractory major depressive disorder. Individualized metabolic differences were found that may help with personalized management.

Associations of potential plasma biomarkers with suicide attempt history, current suicidal ideation and subsequent suicidal events in patients with depression: A discovery study

A growing body of evidences suggests that suicidal ideation (SI) and suicidal behaviors have biological bases. However, no biological marker is currently available to evaluate the suicide risk in individuals with SI or suicide attempt (SA). Moreover, the current risk assessment techniques poorly predict future suicidal events. The aim of this study was to examine the association of 39 new and already described peripheral cells and proteins (implicated in the immune system, oxidative stress and plasticity) with lifetime SA, past month SA, current SI, and future suicidal events (visit to the Emergency Department for SI or SA) in 266 treatment-seeking individuals with mood disorders. Equal parts of patients with and without past history of SA were recruited. All individuals at inclusion gave blood, were evaluated for SA recency, current SI, and were followed for two years afterwards. The 39 peripheral blood cellular and protein markers were entered separately for each outcome in Elastic Net models with 10-fold cross-validation, followed by single-analyte covariate-adjusted regression analyses for pre-selected analytes. Past month SA was associated with increased plasma levels of thrombospondin-2 and C-reactive protein, whereas current SI was associated with lower plasma serotonin levels. These associations were robust to adjustments for key covariates and corrections for multiple testing. The Cox proportional hazards regression showed that higher levels of thrombospondin-1 and of platelet-derived growth factor-AB predicted a future suicidal event. These two associations remained after adjustment for sex, age, and SA history, and outperformed the predictive value of past SA. Thrombospondins and platelet-derived growth factors have never been investigated in the context of suicide. Altogether, our results highlight the involvement in the suicidal process of platelet biological response and plasticity modifiers and also of inflammatory factors. They also suggest that SI and SA may have different biological correlates and that biomarkers associated with past SA or current SI do not automatically also predict future events.

Localization and Diagnostic Specificity of Glutamic Acid Decarboxylase Transcript Alterations in the Dorsolateral Prefrontal Cortex in Schizophrenia

BACKGROUND

Working memory (WM) deficits in schizophrenia are thought to reflect altered inhibition in the dorsolateral prefrontal cortex (DLPFC). This interpretation is supported by findings of lower transcript levels of the 2 enzymes, GAD67 and GAD65, which mediate basal and activity-dependent GABA (gamma-aminobutyric acid) synthesis, respectively. However, the relative magnitude, location within the depth of the DLPFC, and specificity to the disease process of schizophrenia of alterations in GAD67 and/or GAD65 remain unclear.

METHODS

Levels of GAD67 and GAD65 messenger RNAs (mRNAs) in superficial (layers 2/superficial 3) and deep (deep layer 6/white matter) zones of the DLPFC were quantified by quantitative polymerase chain reaction in subjects with schizophrenia (n = 41), major depression (n = 42), or bipolar disorder (n = 39) and unaffected comparison (n = 43) subjects.

RESULTS

Relative to the unaffected comparison group, GAD67 and GAD65 mRNA levels in the schizophrenia group were lower (p = .039, effect size = -0.69 and p = .027, effect size = -0.72, respectively) in the superficial zone but were unaltered in the deep zone. In the major depression group, only GAD67 mRNA levels were lower and only in the superficial zone (p = .089, effect size = 0.70). No differences were detected in the bipolar disorder group. Neither GAD67 nor GAD65 mRNA alterations were explained by psychosis, mood disturbance, or common comorbid factors.

CONCLUSIONS

Alterations in markers of GABA synthesis demonstrated transcript, DLPFC zone, and diagnostic specificity. Given the dependence of WM on GABA neurotransmission in the superficial DLPFC, our findings suggest that limitations to GABA synthesis in this location contribute to WM impairments in schizophrenia, especially during demanding WM tasks, when GABA synthesis requires the activity of both GAD67 and GAD65.

Altered transcriptomes, cell type proportions, and dendritic spine morphology in hippocampus of suicide deaths

Suicide is a condition resulting from complex environmental and genetic risks that affect millions of people globally. Both structural and functional studies identified the hippocampus as one of the vulnerable brain regions contributing to suicide risk. Here, we have identified the hippocampal transcriptomes, gene ontology, cell type proportions, dendritic spine morphology, and transcriptomic signature in iPSC-derived neuronal precursor cells (NPCs) and neurons in postmortem brain tissue from suicide deaths. The hippocampal tissue transcriptomic data revealed that NPAS4 gene expression was downregulated while ALDH1A2, NAAA, and MLXIPL gene expressions were upregulated in tissue from suicide deaths. The gene ontology identified 29 significant pathways including NPAS4-associated gene ontology terms "excitatory post-synaptic potential", "regulation of postsynaptic membrane potential" and "long-term memory" indicating alteration of glutamatergic synapses in the hippocampus of suicide deaths. The cell type deconvolution identified decreased excitatory neuron proportion and an increased inhibitory neuron proportion providing evidence of excitation/inhibition imbalance in the hippocampus of suicide deaths. In addition, suicide deaths had increased dendric spine density, due to an increase of thin (relatively unstable) dendritic spines, compared to controls. The transcriptomes of iPSC-derived hippocampal-like NPCs and neurons revealed 31 and 33 differentially expressed genes in NPC and neurons, respectively, of suicide deaths. The suicide-associated differentially expressed genes in NPCs were RELN, CRH, EMX2, OXTR, PARM1 and IFITM2 which overlapped with previously published results. The previously-known suicide-associated differentially expressed genes in differentiated neurons were COL1A1, THBS1, IFITM2, AQP1, and NLRP2. Together, these findings would help better understand the hippocampal neurobiology of suicide for identifying therapeutic targets to prevent suicide.

The miR-124-AMPAR pathway connects polygenic risks with behavioral changes shared between schizophrenia and bipolar disorder

Schizophrenia (SZ) and bipolar disorder (BP) are highly heritable major psychiatric disorders that share a substantial portion of genetic risk as well as their clinical manifestations. This raises a fundamental question of whether, and how, common neurobiological pathways translate their shared polygenic risks into shared clinical manifestations. This study shows the miR-124-3p-AMPAR pathway as a key common neurobiological mediator that connects polygenic risks with behavioral changes shared between these two psychotic disorders. We discovered the upregulation of miR-124-3p in neuronal cells and the postmortem prefrontal cortex from both SZ and BP patients. Intriguingly, the upregulation is associated with the polygenic risks shared between these two disorders. Seeking mechanistic dissection, we generated a mouse model that upregulates miR-124-3p in the medial prefrontal cortex. We demonstrated that the upregulation of miR-124-3p increases GRIA2-lacking calcium-permeable AMPARs and perturbs AMPAR-mediated excitatory synaptic transmission, leading to deficits in the behavioral dimensions shared between SZ and BP.

Investigating the Clinical Profile of Suicide Attempters Who Used a Violent Suicidal Means

In our study, we aimed to explore the profile of the high-risk subgroup of suicide attempters that used a violent means compared to suicide attempters that chose a non-violent suicide means. Therefore, we recruited a sample of inpatients with recent suicide attempts in three psychiatric hospitals in Thuringia, Germany. We used a structured clinical interview to assess the psychiatric diagnoses, sociodemographic data, and characteristics of the suicide attempt. Furthermore, we used several validated clinical questionnaires to measure suicidal ideations, suicide intent, depression severity, hopelessness, impulsivity, aggression, anger expression, and childhood trauma. We compared 41 individuals using violent means to 59 using non-violent means with univariate and multivariate statistical analyses. We found significantly (corrected for multiple comparisons) higher levels of impulsivity-related sensation-seeking in violent suicide attempters in univariate and multivariate analyses, and additionally in anger expression directed inward at an uncorrected statistical threshold. Besides that, there were no significant differences between the two groups. We assume that underlying neurocognitive mechanisms, such as impaired decision-making processes and/or differences in risk/loss assessment, could explain the higher levels of questionnaire-based sensation-seeking in subjects who use violent suicide means. Further research is needed, including neuroimaging and biochemical techniques, to gain more insight into the mechanisms underlying the choice of a suicidal means.

Transcriptome Profiling of the Dorsomedial Prefrontal Cortex in Suicide Victims

The default mode network (DMN) plays an outstanding role in psychiatric disorders. Still, gene expressional changes in its major component, the dorsomedial prefrontal cortex (DMPFC), have not been characterized. We used RNA sequencing in postmortem DMPFC samples to investigate suicide victims compared to control subjects. 1400 genes differed using log2FC > ±1 and adjusted p-value < 0.05 criteria between groups. Genes associated with depressive disorder, schizophrenia and impaired cognition were strongly overexpressed in top differentially expressed genes. Protein−protein interaction and co-expressional networks coupled with gene set enrichment analysis revealed that pathways related to cytokine receptor signaling were enriched in downregulated, while glutamatergic synaptic signaling upregulated genes in suicidal individuals. A validated differentially expressed gene, which is known to be associated with mGluR5, was the N-terminal EF-hand calcium-binding protein 2 (NECAB2). In situ hybridization histochemistry and immunohistochemistry proved that NECAB2 is expressed in two different types of inhibitory neurons located in layers II-IV and VI, respectively. Our results imply extensive gene expressional alterations in the DMPFC related to suicidal behavior. Some of these genes may contribute to the altered mental state and behavior of suicide victims.