Molecular Psychiatry

Major depressive disorders (MDD) are predicted to become the first cause of burden of disease worldwide in 2030, but 30% of patients still do not respond to antidepressants. Current rodent models of MDD mainly result either from one genetic or one environmental risk factor exposure, not recapitulating the multifactorial and polygenic nature of MDD. We recently generated a polygenic mouse model of MDD from selective breeding after mild stress in the Tail Suspension Test (TST), named H-TST. Here, we selected animals exhibiting high immobility during the Forced Swim Test (FST) to generate a new stable polygenic model of MDD, called H-FST. Unlike our previous H-TST model, H-FST mice did not exhibit any anxiety-or anhedonia-like behaviors, nor did they display any sleep disturbances. Moreover, H-TST and H-FST mice showed opposite response after administration of various antidepressant treatments. The gene expression level in the prefrontal cortex of H-TST and H-FST mice revealed little overlap in genes and biological pathways associated with depressive-like behaviors and opposite dysregulation of excitatory/inhibitory synaptic imbalance. Finally, these two models allowed in humans the identification biomarkers of treatment response specific of clinical subgroup of patients.

Postpartum depression (PPD) arises during a period of profound endocrine and immune reorganisation, yet it is unclear whether women who develop PPD show distinct trajectories of immune-related DNA methylation compared to euthymic mothers. In a longitudinal cohort, women with PPD (n = 17) and healthy postpartum controls (n = 24) were followed from birth to 12 weeks postpartum, with repeated assessment of depressive symptoms and perceived stress and whole-blood sampling at 2-3 days (T0) and 12 weeks (T4) for Infinium MethylationEPIC array profiling. Healthy postpartum women showed a widespread gain in DNA methylation from T0 to T4 with strong enrichment of genes involved in neutrophil activation, chemokine signalling and interleukin-1 production, consistent with a normative immune-epigenetic down-tuning after childbirth. Women with PPD also exhibited immune-related changes, but with fewer differentially methylated CpGs and increased variance at sites that were stably hypermethylated in controls, indicating an attenuated and more heterogeneous epigenetic response. Although no CpG reached epigenome-wide significance in direct case-control contrasts, longitudinal consistency analyses highlighted a small set of CpGs with reproducible PPD-associated hypermethylation in stress- and signalling-related genes, including FKBP5 and AVP, suggesting that disrupted immune-epigenetic adaptation and altered regulation at these loci may contribute to postpartum vulnerability.

Major Depressive Disorder (MDD) frequently follows a recurrent trajectory of episodes and remissions, often culminating in treatment-resistance. Molecular differences defining state-specific changes during episode and remission have been explored. However, progressive differences--defined here as cross-sectional linear trends across clinical stages from first to recurrent episodes or remissions, reflecting increasing illness burden over time--remain poorly understood, limiting sustained therapeutic outcomes. Here, we analyzed RNA-seq data from postmortem sgACC to identify progressive differences across MDD episodes or remission relative to state-specific differences, using an integrative assessment of molecular and cellular specificity, genetic-risk, disease-comorbidity and potential therapeutic targets. Differential expression analysis showed greater overlap between progressive and state-specific differences during remission than episode. Pathway enrichment highlighted disruptions in extracellular-matrix pathways shared by state-specific and progressive episodes, while metabolic and catalytic pathways were restored during remission. Cell-type-specific analyses showed that progressive changes were linked to superficial-layer intra-telencephalic neurons, whereas state-specific changes were enriched in pyramidal neuron subtypes and deeper layer SST-positive interneurons. Genome-wide association-informed enrichment analysis further linked these transcriptomic changes to genetic risk factors and symptom dimensions. Anhedonia was associated with both state-specific episode and progressive-remission signatures, suggesting that it is a persistent trait-like feature of MDD. Finally, an integrative pharmacological analysis revealed shared molecular mechanisms between pro-disease and therapeutic targets, highlighting pleiotropic effects of key pathways depending on disease state and dosage. Together, these findings provide a novel perspective on biological underpinnings of MDD progression over episodes or remissions and identify pharmacological targets that account for pathological and/or compensatory/therapeutic processes.

Cortical inhibitory neurons (CIN) populate the neocortex and hippocampus by extensive tangential migration. This process is highly vulnerable to genetic and environmental disturbances and is linked to neuropsychiatric disorders. However, the mechanisms by which transient migratory abnormalities translate into persistent functional deficits remain poorly understood. Here, we utilized a conditional Cxcr4 knockout to investigate the consequences of disrupted migratory guidance - a feature of genetic schizophrenia models. This demonstrated that despite migrating in ectopic cortical layers, CIN quantitatively colonized the neocortex until birth, whereas limbic regions developed a permanent deficit in CIN numbers. Furthermore, CIN failed to populate the neocortical marginal zone, a transient reservoir for late-born CIN destined for superficial cortical layers. Consequently, the layering and molecular identities of CIN, as well as the synaptic connectivity and spontaneous activity of the neuronal network, were significantly altered in the early postnatal neocortex. Although abnormal CIN layering was gradually compensated before maturity, functional differences persisted, as evidenced by facilitated propagation of sensory stimuli between cortical areas. These results demonstrate that CIN migration is an instructive process critical for activity-driven early postnatal network maturation and CIN identity, thus providing a mechanistic link between migratory guidance and the integrity of mature circuits.

BackgroundThe single nucleotide polymorphism (SNP) rs1053230 within the kynurenine 3-monooxygenase (KMO) gene encodes either an arginine (CGC) or cysteine (TGC) at amino acid residue 452. The rs1053230 genotype is associated with alterations in KMO expression and activity, and impaired cognition. Additionally, KMO intronic SNP rs2275163 is associated with schizophrenia endophenotypes. However, the direct functional consequences of these SNPs on KMO function have never been investigated. MethodsHere we performed the first in vitro cell-based examination of the rs1053230 genotype on KMO expression, activity, cellular localisation and KMO-protein interactions, as well as examination of the effects of rs1053230 on schizophrenia-relevant clinical measures. We also examined the effects of rs2275163 genotype on KMO pre-mRNA stability and alternative splicing. ResultsHEK293T cells expressing KMO-Arg452 or KMO-Cys452 with a red fluorescent protein (RFP) tag produced equivalent levels of KMO mRNA, protein and enzymatic activity, and localised to mitochondria to the same extent. However, cycloheximide-mediated inhibition of protein translation revealed a striking reduction in protein stability of KMO-Arg452-RFP. KMO-RFP-trap pull-down followed by tandem liquid-chromatography-mass spectrometry (LC-MS/MS) identified dramatic differences in protein partners between KMO variants. Indeed, gene ontology-term enrichment analysis revealed that terms associated with synaptic function were more highly enriched amongst KMO-Cys452 interacting proteins. rs1053230 genotype was found to associate with chronic, trait-like depressive mood symptoms in patients. rs2275163 genotype had no effect on KMO pre-mRNA. ConclusionsDifferences in protein stability and protein-protein interactions may underlie the mechanisms by which the KMO rs1053230 genotype influences neuronal function, leading to cognitive differences in psychiatric conditions.

Schizophrenia is a severe psychiatric disorder associated with altered dopaminergic signaling and hippocampal circuit dysfunction. Although antipsychotic medications remain the standard treatment, many are limited by incomplete efficacy and adverse effects. Cariprazine, a dopamine D2/D3 receptor partial agonist, has a favorable clinical profile, but its effects on neuronal excitability and network activity remain incompletely understood. Here, we integrated nationwide real-world clinical data with in vitro electrophysiology, computational modeling, and molecular analyses to define the neuronal actions of cariprazine. Among Hungarian patients diagnosed with schizophrenia and receiving index-drug monotherapy with one of the three prespecified D2/D3 targeting antipsychotics, haloperidol was associated with worse survival and a higher cumulative incidence of first registered suicide attempt than cariprazine or aripiprazole in matched observational cohorts. In primary mouse hippocampal cultures, multielectrode array recordings showed that acute cariprazine treatment moderately reduced spontaneous firing in a dose-dependent manner and prolonged burst intervals while largely preserving network synchronization. These effects were milder than those of haloperidol and aripiprazole. Whole-cell patch-clamp recordings revealed cell-type-dependent effects, with reduced intrinsic excitability and increased firing irregularity mainly in regular- and stuttering-type neurons. Conductance-based modeling identified enhanced Kv1-mediated D-type potassium currents as sufficient to reproduce these effects. Consistent with this mechanism, chronic cariprazine treatment altered Kv1.2 protein distribution without changing Kcna2/Kcna3 or Drd1/Drd2/Drd3 transcript expression. These findings identify modulation of intrinsic excitability via Kv1/D-type potassium currents as a candidate cellular mechanism of cariprazine and provide a translational link between real-world evidence and circuit-level drug effects.

Mutations in SCN2A, which encodes the voltage-gated sodium channel Nav1.2, are associated with a wide spectrum of neurodevelopmental and neuropsychiatric disorders, including epilepsy, autism spectrum disorder (ASD), and schizophrenia. Although dysfunction of SCN2A-dependent neural circuits has been implicated in these disorders, the circuit mechanisms underlying social behavioral abnormalities remain poorly understood. Here, we investigated the neural circuit basis of social behavioral deficits associated with Scn2a dysfunction, focusing on the nucleus accumbens (NAc), a key hub in cortico-limbic circuits that regulates emotional and motivational behaviors. Using conditional genetic and chemogenetic approaches in mice, we examined the roles of dorsal telencephalic excitatory neurons, including those in the cerebral cortex, hippocampus, and amygdala, as well as parvalbumin-positive fast-spiking interneurons (PV FSIs) in the NAc. Mice with Scn2a haploinsufficiency in dorsal telencephalic excitatory neurons (Scn2afl/+/Emx1-Cre) exhibited reduced sociability in the three-chamber social interaction test. Similarly, chemogenetic inhibition of NAc PV FSIs decreased sociability without affecting locomotor activity or anxiety-like behavior. Scn2afl/+/Emx1-Cre mice also showed a trend toward reduced prepulse inhibition of the acoustic startle response. Notably, dopamine release into the NAc in the Scn2afl/+/Emx1-Cre and systemic Scn2a heterozygous knockout (Scn2a+/-) mice was largely comparable to that in control mice. Together, these findings indicate that reduced activity of dorsal telencephalic excitatory neurons or NAc PV FSIs is sufficient to impair sociability independently of mesolimbic dopamine hypofunction. Our results highlight a potential role of cortico-accumbal circuits in social behavioral deficits associated with SCN2A dysfunction.

Schizophrenia (SCZ) is increasingly linked to neuroimmune dysregulation and impaired synaptic plasticity, yet the cellular mechanisms connecting inflammatory signaling to neural dysfunction remain poorly understood. Using human induced pluripotent stem cell (iPSC)-derived cortical spheroids (hCS) and astrocytes from patients with SCZ and matched controls, we investigated the effects of GABAA receptor modulation on immune signaling and neuroplasticity. Inflammatory stimulation induced robust interferon-responsive transcriptional programs, prominently involving the antiviral effector MX1 and related interferon-stimulated genes. Computational deconvolution and cell type-specific analyses identified astrocytes as key mediators of these responses. Muscimol, a non-classic psychedelic and GABAA receptor agonist, suppressed inflammatory gene expression, reduced secretion of proinflammatory cytokines, and attenuated interferon-associated signaling. In addition, muscimol induced neuroplasticity-associated transcriptional programs, including upregulation of NTRK2 and ELK1 in hCSs, and restored impaired glutamate uptake in iPSC-derived SCZ astrocytes. These effects were blocked by GABAA receptor inhibition, confirming receptor-dependent mechanisms. Proteomic analyses of hCS cultures, and independent human dorsolateral prefrontal cortex datasets revealed baseline dysregulation of GABAergic and neurotrophin signaling in SCZ, supporting translational relevance. Together, these findings demonstrate that GABAA receptor activation by muscimol suppresses inflammatory signaling while promoting neuroplasticity in hCSs, and identify astrocytes as central regulators of interferon-dependent neuroimmune dysfunction in SCZ. These results establish non-classic psychedelic compounds as potential modulators of neuroimmune-plasticity coupling and suggest that targeting astrocyte GABAergic signaling may represent a therapeutic strategy for restoring neural homeostasis in SCZ.

Schizophrenia (SZ) arises from complex gene-environment interactions, yet how early insults shape later circuit vulnerability remains unclear. Here, we investigated whether bioenergetic states represent a convergent disease signature across genetic and environmental risk factors. We analyzed transcriptional profiles across neocortical development in murine models of maternal immune activation (polyIC MIA), and serine racemase deletion (Srr-/-), extending these analyses to juvenile stages in Srr-/- and interneuron-specific NMDA receptor deletion (Nkx2.1:Grin1fl/fl), highlighting cell-type-specific metabolic vulnerability across developmental stages. In MIA, early gestation (E12.5) revealed a transient bioenergetic shift likely driven by microglial and radial glial populations, suggesting metabolic priming rather than canonical inflammatory signaling. By late gestation (E17.5), MIA induced coordinated dysregulation of neuronal glycolytic isoforms alongside mitochondrial and lipid-associated metabolic pathways, suggesting coordinated metabolic remodeling involving lipid-linked processes. In contrast, Srr-/- mice showed minimal glycolytic alterations at E17.5, indicating that isolated genetic perturbation is insufficient to recapitulate this fetal metabolic state. However, at juvenile stages, region-specific bioenergetic adaptations emerged. Srr-/- mice exhibited global cortical increases in glycolytic gene expression, with hippocampal changes potentially enriched in neuronal populations. Conversely, Nkx2.1:Grin1fl/flinterneurons showed increased glycolytic and TCA cycle transcription in the hippocampus but opposing patterns in the medial prefrontal cortex. Together, these findings identify increased glycolytic activity, potentially linked to lactate metabolism, as a partially convergent developmental mechanism bridging prenatal perturbations and later circuit dysfunction in SZ, and suggest that downstream glycolysis-linked pathways may contribute to phenotypic heterogeneity. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=174 SRC="FIGDIR/small/723970v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@1dd1461org.highwire.dtl.DTLVardef@1651b65org.highwire.dtl.DTLVardef@e98bc8org.highwire.dtl.DTLVardef@d813a2_HPS_FORMAT_FIGEXP M_FIG C_FIG

Antidepressants are widely prescribed for major depressive disorder, yet only one-third of patients achieve remission after initial treatment. Previous genome-wide association studies (GWAS) of clinically assessed antidepressant response combined multiple antidepressant classes, potentially obscuring class-specific effects. This study focused on selective serotonin reuptake inhibitors (SSRIs), often first-line due to better tolerability. Data from 15 cohorts across four ancestries were integrated: European (N = 3887; 11 studies), East Asian (N = 1068; 4), African (N = 277; 1), and Admixed American (N = 250; 1). GWAS of non-remission and percentage improvement were conducted within cohorts, followed by ancestry-specific meta-analyses and trans-ancestry meta-regression. Single nucleotide polymorphism (SNP)-based heritability was estimated in European samples. Polygenic scores were used for leave-one-out prediction and to assess shared genetic architecture with psychiatric traits. Gene-level and gene-set enrichment analyses were also performed. No genome-wide significant variants were identified for either outcome in any ancestry-specific or trans-ancestry analyses. However, trans-ancestry meta-regression yielded eight independent loci with suggestive associations (p < 1 x 10-5) for non-remission and 17 for percentage improvement. Gene-set analyses revealed nominal enrichment of the serotonergic synapse pathway for non-remission. SNP-based heritability estimates were not significantly different from zero for either outcome. Better SSRI response was nominally associated with lower genetic predisposition to major depressive disorder, post-traumatic stress disorder, and schizophrenia. This study represents the largest trans-ancestry GWAS of SSRI response, highlighting emerging biological signals. Limited power emphasises the need for larger and ancestrally diverse cohorts to better characterise the genetic architecture of antidepressant response.

Psychedelics show therapeutic potential for treating psychiatric disorders. While studies have emphasized the roles of cortical pyramidal cells, GABAergic neurons also express serotonin receptors and are therefore likely targets of psychedelics. In this study, we determine the effect of psilocybin on the activity dynamics of major GABAergic cell types in the mouse medial frontal cortex. Psilocybin reduces the firing of somatostatin-expressing interneurons, but increases the activity of parvalbumin-expressing interneurons. This cell type-specific response is unlikely to involve vasoactive intestinal peptide-expressing interneurons. Instead, pharmacological blockade and conditional knockout experiments demonstrate that psilocybin acts on the 5-HT1A receptor at SST interneurons, which contributes to the drugs long-term behavioral effects. Collectively, the results reveal that the classic psychedelic psilocybin alters cortical inhibition in a cell type-specific manner.

The 7-nicotinic acetylcholine receptor (7nAChR) has driven extensive research over the past three decades for its pro-cognitive potential. It is the leading druggable target for the cognitive deficits associated with schizophrenia and has motivated major pharmaceutical and clinical efforts to ameliorate similar impairments in other neurological disorders, such as Alzheimers disease (AD). Yet, a systematic evaluation of the role played by 7nAChR in cognition, and its mechanistic underpinnings, is still lacking. Here we report that 7nAChRs on principal and inhibitory forebrain neurons are largely inconsequential to mouse behavior, including in domains that are most sensitive to schizophrenia-related cognitive impairments. By contrast, loss of 7nAChR from astrocytes produces profound behavioral alterations that are cognitive domain-specific, are time-of-day dependent, coincide with reduced levels of the N-methyl D-aspartate receptor (NMDAR) co-agonist D-serine, and are fully restored by D-serine supplementation. Further, an 7nAChR partial agonist previously evaluated in Phase III trials for cognitive enhancement in schizophrenia and AD fails to augment behavior in mice lacking astrocytic 7nAChRs. Together, these findings identify astrocytes and D-serine/NMDAR signaling as a central mechanism through which 7nAChR, a major drug target, promotes cognitive behavior.

Leucine-rich repeat-containing 8 (LRRC8) proteins form the volume-regulated anion channel (VRAC) and participate in diverse physiological processes, including cell volume regulation, gliotransmitter release, and insulin secretion. In mammals, five paralogs (LRRC8A-E) exist; LRRC8A is the obligatory subunit that assembles into functional hexameric channels with LRRC8C, D, or E. LRRC8B is distinct: we previously demonstrated its role in regulating endoplasmic reticulum (ER) Ca{superscript 2} homeostasis and ER Ca{superscript 2} leak. A LRRC8B variant (Y380S) identified in an Indian family with severe mental illness has been associated with disease pathology, but its molecular and cellular consequences remain unknown. Here, we show that this disease-associated mutant perturbs Ca{superscript 2} signalling, mitochondrial bioenergetics, and redox homeostasis. Both wild-type and mutant LRRC8B localize to the ER and mitochondria. LRRC8B knockdown significantly reduced mitochondrial Ca{superscript 2} uptake and maximal respiratory the Y380S mutant phenocopied LRRC8B knockdown, altering ER Ca{superscript 2} release, elevating basal cytosolic Ca{superscript 2}, and impairing mitochondrial Ca{superscript 2} uptake, consistent with a dominant-negative mechanism. The mutant further induced mitochondrial dysfunction, including loss of membrane potential, oxidative stress, and defective antioxidant responses, ultimately compromising cellular bioenergetics and viability. Mechanistically, the Y380S mutation disrupted LRRC8B interaction with the mitochondrial outer membrane channel VDAC. These findings identify LRRC8B-VDAC coupling as a key determinant of mitochondrial Ca{superscript 2} handling and provide a mechanistic link between LRRC8B dysfunction and neuropsychiatric disease. HighlightsO_LIA psychiatric disease-associated LRRC8B variant (Y380S) acts as a dominant-negative regulator of ER Ca{superscript 2} homeostasis. It enlarges the releasable ER Ca{superscript 2} pool and reduces cell viability. C_LIO_LILRRC8B promotes mitochondrial Ca{superscript 2} uptake through interaction with VDAC. The Y380S mutation disrupts this interaction, reducing mitochondrial Ca{superscript 2} uptake. C_LIO_LIThe Y380S mutant increases mitochondrial superoxide production without activating compensatory antioxidant responses. C_LIO_LIThe mutant also causes mitochondrial membrane depolarization and bioenergetic failure, as evidenced by reduced oxygen consumption rate and ATP production. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=140 SRC="FIGDIR/small/718892v1_ufig1.gif" ALT="Figure 1"> View larger version (47K): org.highwire.dtl.DTLVardef@1f314d3org.highwire.dtl.DTLVardef@1dc3908org.highwire.dtl.DTLVardef@124445aorg.highwire.dtl.DTLVardef@39326_HPS_FORMAT_FIGEXP M_FIG C_FIG

Weak inhibition of mitochondrial complex I (mtCI) has been shown to have neuroprotective effects in cellular and animal models of Alzheimers and Huntingtons diseases, at least in part by enhancing mitochondrial biogenesis and function. Mitochondrial dysfunction has also been demonstrated in schizophrenia patients and mouse models of schizophrenia. We tested whether weak inhibition of mtCI would ameliorate mitochondrial and behavioral phenotypes in a mouse model of schizophrenia. In mice with four copies of the Gldc gene, 8 weeks of treatment with the weak mtCI inhibitor, the small-molecule tricyclic pyrone compound CP2, reversed spontaneous alternation deficits in the Y maze, startle habituation deficits, and social novelty deficits in the three-chamber social interaction test. Consistent with the mechanism of action, Western blots revealed that CP2 reverses the reduced expression of PGC-1, a master regulator of mitochondrial biogenesis, and of the VDAC1, a primary gatekeeper for the exchange of metabolites, ions, and ATP between mitochondria and the cytosol. These findings suggest that the improvement of mitochondrial function may represent a novel strategy to reverse pathophysiological and behavioral deficits in schizophrenia.

Antipsychotic drugs are the first-line treatment for psychosis yet their mechanism of action remains poorly understood, largely due to the challenge to faithfully model psychosis preclinically. Here, we focus on the emerging concept that psychosis can be caused by brain autoimmunity and present a novel mouse model of anti-N-methyl-D-aspartate-receptor (anti-NMDAR) encephalitis, a condition that manifests with psychosis and autoanti-bodies against the NMDAR. We devised a new mRNA-based approach to immunize mice against the NMDAR. Immunized mice developed psychosis-like behaviors that were caused by anti-NMDAR autoantibodies leading to phagocytosis of NMDARs by brain microglia. The antipsychotic drug clozapine rescued psychosis-like behaviors and, remarkably, reduced anti-NMDAR autoantibody levels and antibody-mediated phagocytosis of NMDARs. The immunomodulatory effects of clozapine were confirmed in a mouse model of systemic lupus erythematosus. Our results demonstrate that clozapine suppresses autoimmunity driving psychosis-like behaviors, raising the possibility that immunomodulation contributes to antipsychotic drug action. HIGHLIGHTSO_LImRNA immunization against the NMDAR induces psychosis-like behavior in mice C_LIO_LIAnti-NMDAR autoantibodies are sufficient for psychosis-like behavior C_LIO_LIMicroglial phagocytosis of NMDARs mediates psychosis-like behavior induced by anti-NMDAR autoanti-bodies. C_LIO_LIClozapine reduces anti-NMDAR autoantibodies, microglial phagocytosis and psychosis-like behavior, consistent with immunomodulation as a potential mechanism of antipsychotic drug action. C_LI

The hippocampal formation (HPF) provides neural substrates integrating disparate sensory cues into episodic memories and coherent action. Whereas HPF structures are formed by birth, the functional circuits evolve over postnatal development. Our previous studies showed that transient perinatal expression of the serotonin (5-HT) transporter SERT/Slc6a4 in CA3 pyramidal neurons, which do not synthesize 5-HT but take up extracellular 5-HT thus termed "5-HT-absorbing neurons", exerts sex-biased effects on long-term activity-dependent HPF synaptic plasticity and behavior in mice. This study investigates SERT impact on circuit development, through single-nucleus transcriptomics of postnatal HPF from CA3-pyramidal neuron SERT knockout (SERTPyramid{Delta}) mice. We demonstrate that SERTPyramid{Delta} mice preserve cell identities across the HPF but alter gene expression in specific neuronal types in a sex-biased manner. We observed SERTPyramid{Delta} male-biased upregulation of genes preferentially in glutamatergic neurons, particularly affecting the CA2 and parasubiculum (PaS) when they develop social novelty and spatial representations, respectively. In both the CA2 and PaS, altered genes center on two categories -- modulators of gene expression patterning including chromatin plasticity, RNA processing and ubiquitin-dependent protein degradation, and aspects of synaptic transmission. >20% of the dysregulated genes in the CA2 and PaS are associated with Autism and engaged in cell-type distinct functional networks, showing CA3 SERT regulation of ASD-vulnerable genes in intersecting biological processes in specific neurons during social and spatial circuits development. The data, available at https://scviewer.shinyapps.io/hippocampus_sertKO, provide an entry map for further deducing anatomical neuronal origin and the molecular and cellular pathways impaired by 5-HT dysfunction during HPF circuits development leading to lifetime cognitive deficits.

Genomic insights into psychiatric disorders remain heavily skewed toward European populations. In European-ancestry studies, educational attainment is typically negatively genetically correlated with major depression but paradoxically positively correlated with schizophrenia, raising the question of whether these relationships generalize across ancestries. We investigated whether this cross-trait architecture extends to East Asian ancestry (EAS). Using EAS GWAS summary statistics for major depressive disorder (MDD), schizophrenia (SZ), and educational attainment (EDU), we applied multi-trait (MTAG) and pleiotropy-informed (PLEIO) analyses to characterize shared genetic architecture across these traits. Across MTAG and PLEIO analyses, we identified 32 unique genome-wide significant loci (p < 5 x 10-8), including seven novel loci revealed in depression analysis that overlapped schizophrenia-associated signals, consistent with shared cross-trait architecture. Results reinforce a convergent risk architecture for affective and psychotic disorders in this population. Fine-mapping analyses prioritized variants mapping to candidate genes, including serine/threonine kinase VRK2, nominating targets for future follow-up. Cross-trait analyses supported a positive genetic relationship between EDU and MDD (rg = 0.308, p = 9.63 x 10-17) in East Asian data, contrasting to the negative correlation typically observed in European ancestry. These findings suggest that the genetic relationship between educational attainment and psychiatric risk may not be fully transferable across ancestries. In an independent cohort of individuals at ultra-high risk for psychosis, MTAG-derived polygenic risk scores improved case-control discrimination relative to single-trait GWAS-based scores. These results underscore the importance of ancestry-specific genomic frameworks for interpreting cross-trait psychiatric architecture and improving polygenic prediction.

Thirty-five percent of people with schizophrenia-related disorders (SRD) form a high-inflammation subgroup defined by elevated anti-gliadin antibodies (AGA+) and inflammatory proteins and associated with an increased severity of negative symptoms. However, the immune mechanisms mediating these effects remain poorly defined. Here, we characterized transcriptional signatures of peripheral immune cells in AGA+ SRD (n=7) compared to AGA-negative (AGA-) SRD (n=3) and healthy controls (HC; n=5), using single-cell RNA-sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs). AGA+ SRD was associated with increased abundance of T-helper-17 cells (Th17), T-follicular helper-1 (Tfh1), CD5+ B cells, plasmacytoid dendritic cells (pDCs), and several CD8+ T cell subsets, including memory and Natural Killer-T-like activated subsets. In parallel, AGA-SRD exhibited a higher abundance of several monocyte subsets compared to either AGA+ SRD or HC. Pathway analysis revealed upregulation in AGA+ SRD of JAK/STAT, type I Interferon, and IL-6 signaling pathways in distinct subset of activated T-cells. Collectively, these results define a unique T cell predominant inflammatory signature in AGA+ SRD, as well as potential targets for therapeutic intervention.

Background: Major depressive disorder (MDD) is characterized by disrupted information flow among brain regions. While effective connectivity (EC) captures these causal interactions, the underlying structural and molecular basis remain unclear. This study aims to investigate direction-specific EC alterations in MDD and their associations with laminar structural covariance (SC) and transcriptional and neurotransmitter profiles. Methods: Resting-state fMRI and structural MRI data were analyzed from the REST-meta-MDD consortium (Discovery, N=1627) and an independent cohort (Validation, N=226). We calculated the unsigned and signed EC using Liang Information Flow and laminar SC based on cortical depth, and compared them between MDD patients and healthy controls. The EC alterations were further associated with molecular profiles integrating gene expression (AHBA) and neurotransmitter receptors (PET/SPECT). Then, Chain mediation analyses were performed to map the hierarchical pathways from molecular basis to EC. Finally, we evaluated the clinical potential of EC in its therapeutic responses to medication and neuromodulation in a longitudinal dataset (N = 16 for medication, N = 11 for neuromodulation). Results: Our analysis revealed no significant changes in the EC of first-episode MDD but observed a hyper-driven cerebellar-cerebral EC pattern in recurrent MDD (RMDD), characterized by a direction-specific excitation-inhibition imbalance featuring enhanced inhibitory cerebellar output alongside a concurrent increase in both inhibitory input and excitatory output within sensorimotor/cognitive regions. These alterations were physically constrained by specific laminar SC patterns, particularly involving the middle cortical lamina. Moreover, the input EC changes in RMDD patients were primarily enriched in biological processes related to the modulation of chemical synaptic transmission, whereas output EC changes were linked to synapse structure regulation. These EC alterations were closely associated with serotonergic, GABAergic, and glutamatergic neurotransmitter systems. Importantly, we identified oligodendrocyte precursor cells (OPCs) as a key cellular mediator bridging microscale molecular features to macroscale connectional alterations in RMDD. These findings were reproducible in the validation dataset. Clinically, medication treatment primarily evoked a pattern of decreased input coupled with increased output, whereas neuromodulation elicited a reciprocal shift characterized by enhanced input and attenuated output. Conclusions: These findings underscore a direction-specific gene-neurotransmitter-cell type-laminar SC-EC pathological model in RMDD. By integrating multi-scale biological mechanisms with clinical phenotypes, this study highlights the potential of directional EC as a biomarker for stratifying refractory depression and guiding precision therapeutics.

GABAergic deficit is associated with key neuropsychiatric disorders, such as major depressive disorder (MDD), anxiety, schizophrenia, and autism spectrum disorder (ASD). However, it is not known whether these disorders are causal to or a result of GABAergic dysfunction. We previously showed that the Solute carrier 38 member 1 (Slc38a1) accumulates glutamine in subpopulations of GABAergic neurons and sustains neurotransmitter GABA synthesis. Genetic inactivation of Slc38a1 in mice caused lowered GABA levels, altered synaptic vesicle morphology, slowed {gamma}-oscillations, and reduced cortical processing and plasticity, selectively at GABAergic synapses. We now demonstrate a significant reduction in learning and memory performance in the Morris water maze and increased signs of despair in the forced swim test in Slc38a1-/- mice compared to Slc38a1+/+ mice, implicating cognitive impairments and depressive-like behavior. Examination in the open field maze also indicates anxiety and/or reduced interest in exploration. There are no signs of impaired sociability or recognition of social novelty in the three-chambered test, speaking against involvement in schizophrenia- or ASD-like disorders. Metabolic phenotyping and measurement of the locomotion do not segregate the Slc38a1 genotypes, suggesting that the cognitive impairments, depressive-like behavior and anxiety are brain-dependent. Our data is further supported by a pathologic variant of Slc38a1 in a family with depression and suicidal behavior. Altogether, we demonstrate that dysfunction of Slc38a1-dependent GABA synthesis and the ensuing impaired {gamma}-oscillations underpin the pathogenesis of neurocognitive deficits, anxiety and depression.