Impact of the DISC1 Ser704Cys polymorphism on risk for major depression, brain morphology and ERK signaling

Astrocyte-mediated regulation of BLAWFS1 neurons alleviates risk-assessment deficits in DISC1-N mice

Assessing and responding to threats is vital in everyday life. Unfortunately, many mental illnesses involve impaired risk assessment, affecting patients, families, and society. The brain processes behind these behaviors are not well understood. We developed a transgenic mouse model (disrupted-in-schizophrenia 1 [DISC1]-N) with a disrupted avoidance response in risky settings. Our study utilized single-nucleus RNA sequencing and path-clamp coupling with real-time RT-PCR to uncover a previously undescribed group of glutamatergic neurons in the basolateral amygdala (BLA) marked by Wolfram syndrome 1 (WFS1) expression, whose activity is modulated by adjacent astrocytes. These neurons in DISC1-N mice exhibited diminished firing ability and impaired communication with the astrocytes. Remarkably, optogenetic activation of these astrocytes reinstated neuronal excitability via D-serine acting on BLAWFS1 neurons' NMDA receptors, leading to improved risk-assessment behavior in the DISC1-N mice. Our findings point to BLA astrocytes as a promising target for treating risk-assessment dysfunctions in mental disorders.

Translational bioinformatics and data science for biomarker discovery in mental health: an analytical review

Translational bioinformatics and data science play a crucial role in biomarker discovery as it enables translational research and helps to bridge the gap between the bench research and the bedside clinical applications. Thanks to newer and faster molecular profiling technologies and reducing costs, there are many opportunities for researchers to explore the molecular and physiological mechanisms of diseases. Biomarker discovery enables researchers to better characterize patients, enables early detection and intervention/prevention and predicts treatment responses. Due to increasing prevalence and rising treatment costs, mental health (MH) disorders have become an important venue for biomarker discovery with the goal of improved patient diagnostics, treatment and care. Exploration of underlying biological mechanisms is the key to the understanding of pathogenesis and pathophysiology of MH disorders. In an effort to better understand the underlying mechanisms of MH disorders, we reviewed the major accomplishments in the MH space from a bioinformatics and data science perspective, summarized existing knowledge derived from molecular and cellular data and described challenges and areas of opportunities in this space.

Evidence of DISC1 as an arsenic binding protein and implications regarding its role as a translational activator

Disrupted-in-schizophrenia-1 (DISC1) is a scaffolding protein that plays a pivotal role in orchestrating signaling pathways involved in neurodevelopment, neural migration, and synaptogenesis. Among those, it has recently been reported that the role of DISC1 in the Akt/mTOR pathway can shift from a global translational repressor to a translational activator in response to oxidative stress induced by arsenic. In this study we provide evidence that DISC1 can directly bind arsenic via a C-terminal cysteine motif (C-X-C-X-C). A series of fluorescence-based binding assays were conducted with a truncated C-terminal domain construct of DISC1 and a series of single, double, and triple cysteine mutants. We found that arsenous acid, a trivalent arsenic derivative, specifically binds to the C-terminal cysteine motif of DISC1 with low micromolar affinity. All three cysteines of the motif are required for high-affinity binding. Electron microscopy experiments combined with in silico structural predictions reveal that the C-terminal of DISC1 forms an elongated tetrameric complex. The cysteine motif is consistently predicted to be located within a loop, fully exposed to solvent, providing a simple molecular framework to explain the high-affinity of DISC1 toward arsenous acid. This study sheds light on a novel functional facet of DISC1 as an arsenic binding protein and highlights its potential role as both a sensor and translational modulator within Akt/mTOR pathway.

Evidence of Disrupted-in Schizophrenia 1 (DISC1) as an arsenic binding protein and implications regarding its role as a translational activator

Disrupted-in-schizophrenia-1 (DISC1) is a scaffold protein that plays a pivotal role in orchestrating signaling pathways involved in neurodevelopment, neural migration, and synaptogenesis. Among those, it has recently been reported that the role DISC1 in the Akt/mTOR pathway can shift from a global translational repressor to a translational activator in response to oxidative stress induced by arsenic. In this study we are providing evidence that DISC1 can directly bind arsenic via a C-terminal cysteine motif (C-X-C-X-C). A series of fluorescence-based binding assays were conducted with a truncated C-terminal domain construct of DISC1 and a of series of single, double, and triple cysteine mutants. We found that arsenous acid, a trivalent arsenic derivative, specifically binds to the C-terminal cysteine motif of DISC1 with low micromolar affinity. All three cysteines of the motif are required for high-affinity binding. Electron microscopy experiments combined with in silico structural predictions revealed that that the C-terminal of DISC1 forms an elongated tetrameric complex. The cysteine motif is consistently predicted to be located within a loop, fully exposed to solvent, providing a simple molecular framework to explain the high-affinity of DISC1 toward arsenous acid. This study sheds light on a novel functional facet of DISC1 as an arsenic binding protein and highlights its potential role as both a sensor and translational modulator within the Akt/mTOR pathway.

Dysregulated Signaling at Postsynaptic Density: A Systematic Review and Translational Appraisal for the Pathophysiology, Clinics, and Antipsychotics' Treatment of Schizophrenia

Emerging evidence from genomics, post-mortem, and preclinical studies point to a potential dysregulation of molecular signaling at postsynaptic density (PSD) in schizophrenia pathophysiology. The PSD that identifies the archetypal asymmetric synapse is a structure of approximately 300 nm in diameter, localized behind the neuronal membrane in the glutamatergic synapse, and constituted by more than 1000 proteins, including receptors, adaptors, kinases, and scaffold proteins. Furthermore, using FASS (fluorescence-activated synaptosome sorting) techniques, glutamatergic synaptosomes were isolated at around 70 nm, where the receptors anchored to the PSD proteins can diffuse laterally along the PSD and were stabilized by scaffold proteins in nanodomains of 50-80 nm at a distance of 20-40 nm creating "nanocolumns" within the synaptic button. In this context, PSD was envisioned as a multimodal hub integrating multiple signaling-related intracellular functions. Dysfunctions of glutamate signaling have been postulated in schizophrenia, starting from the glutamate receptor's interaction with scaffolding proteins involved in the N-methyl-D-aspartate receptor (NMDAR). Despite the emerging role of PSD proteins in behavioral disorders, there is currently no systematic review that integrates preclinical and clinical findings addressing dysregulated PSD signaling and translational implications for antipsychotic treatment in the aberrant postsynaptic function context. Here we reviewed a critical appraisal of the role of dysregulated PSD proteins signaling in the pathophysiology of schizophrenia, discussing how antipsychotics may affect PSD structures and synaptic plasticity in brain regions relevant to psychosis.

Towards an understanding of the pathological basis of senile depression and incident dementia: Implications for treatment

Senile depression (SD) is a heterogeneous syndrome. Several clinical profiles are more likely to appear in SD than in early-life depression, but it remains unclear whether the pathophysiology is different. The prevalence of dementia increases with aging, and the underlying pathophysiological processes in the preclinical phase begin even before cognitive deficits or neurological signs appear. SD may be either a risk factor for developing dementia or a prodromal stage of dementia. The inconsistent findings regarding the association between SD and incident dementia may be attributable to the neuropathological heterogeneity underlying SD. Most studies have focused on patients with the clinical diagnosis of Alzheimer disease (AD) as an outcome, but several clinicopathological studies suggest that primary age-related tauopathy and argyrophilic grain disease may account for a proportion of cases clinically misdiagnosed as AD in the elderly population. Furthermore, most AD cases have additional neuropathologic changes such as cerebrovascular disease and Lewy body disease. Here, we review the neuropathological findings linking SD to incident dementia, focusing on common age-related neuropathologies. In particular, the roles of disturbance of neural circuity, imbalance of monoaminergic systems, dysregulation of the hypothalamic-pituitary-adrenal axis, and elevated neuroinflammatory status are discussed. Finally, we review the current treatment of SD in the context of age-related neuropathological changes.

Social anhedonia as a Disrupted-in-Schizophrenia 1-dependent phenotype

Deficits in social interaction or social cognition are key phenotypes in a variety of chronic mental diseases, yet, their modeling and molecular dissection are only in their infancy. The Disrupted-in-Schizophrenia 1 (DISC1) signaling pathway is considered to play a role in different psychiatric disorders such as schizophrenia, depression, and biopolar disorders. DISC1 is involved in regulating the dopaminergic neurotransmission in, among others, the mesolimbic reward system. A transgenic rat line tgDISC1 has been introduced as a model system to study behavioral phenotypes associated with abnormal DISC1 signaling pathways. Here, we evaluated the impact of impaired DISC1 signaling on social (social interaction) and non-social (sucrose) reward preferences in the tgDISC1 animal model. In a plus-maze setting, rats chose between the opportunity for social interaction with an unfamiliar juvenile conspecific (social reward) or drinking sweet solutions with variable sucrose concentrations (non-social reward). tgDISC1 rats differed from wild-type rats in their social, but not in their non-social reward preferences. Specifically, DISC1 rats showed a lower interest in interaction with the juvenile conspecific, but did not differ from wild-type rats in their preference for higher sucrose concentrations. These results suggest that disruptions of the DISC1 signaling pathway that is associated with altered dopamine transmission in the brain result in selective deficits in social motivation reminiscent of phenotypes seen in neuropsychiatric illness.

Mutations in DISC1 alter IP3R and voltage-gated Ca2+ channel functioning, implications for major mental illness

Disrupted in Schizophrenia 1 (DISC1) participates in a wide variety of developmental processes of central neurons. It also serves critical roles that underlie cognitive functioning in adult central neurons. Here we summarize DISC1’s general properties and discuss its use as a model system for understanding major mental illnesses (MMIs). We then discuss the cellular actions of DISC1 that involve or regulate Ca²⁺ signaling in adult central neurons. In particular, we focus on the tethering role DISC1 plays in transporting RNA particles containing Ca²⁺ channel subunit RNAs, including IP3R1, CACNA1C and CACNA2D1, and in transporting mitochondria into dendritic and axonal processes. We also review DISC1’s role in modulating IP₃R1 activity within mitochondria-associated ER membrane (MAM). Finally, we discuss DISC1-glycogen synthase kinase 3β (GSK3β) signaling that regulates functional expression of voltage-gated Ca²⁺ channels (VGCCs) at central synapses. In each case, DISC1 regulates the movement of molecules that impact Ca²⁺ signaling in neurons.

Conformational heterogeneity coupled with β-fibril formation of a scaffold protein involved in chronic mental illnesses

Chronic mental illnesses (CMIs) pose a significant challenge to global health due to their complex and poorly understood etiologies and hence, absence of causal therapies. Research of the past two decades has revealed dysfunction of the disrupted in schizophrenia 1 (DISC1) protein as a predisposing factor involved in several psychiatric disorders. DISC1 is a multifaceted protein that serves myriads of functions in mammalian cells, for instance, influencing neuronal development and synapse maintenance. It serves as a scaffold hub forming complexes with a variety (~300) of partners that constitute its interactome. Herein, using combinations of structural and biophysical tools, we demonstrate that the C-region of the DISC1 protein is highly polymorphic, with important consequences for its physiological role. Results from solid-state NMR spectroscopy and electron microscopy indicate that the protein not only forms symmetric oligomers but also gives rise to fibrils closely resembling those found in certain established amyloid proteinopathies. Furthermore, its aggregation as studied by isothermal titration calorimetry (ITC) is an exergonic process, involving a negative enthalpy change that drives the formation of oligomeric (presumably tetrameric) species as well as β-fibrils. We have been able to narrow down the β-core region participating in fibrillization to residues 716-761 of full-length human DISC1. This region is absent in the DISC1^Δ22aa splice variant, resulting in reduced association with proteins from the dynein motor complex, viz., NDE-like 1 (NDEL1) and lissencephaly 1 (LIS1), which are crucial during mitosis. By employing surface plasmon resonance, we show that the oligomeric DISC1 C-region has an increased affinity and shows cooperativity in binding to LIS1 and NDEL1, in contrast to the noncooperative binding mode exhibited by the monomeric version. Based on the derived structural models, we propose that the association between the binding partners involves two neighboring subunits of DISC1 C-region oligomers. Altogether, our findings highlight the significance of the DISC1 C-region as a crucial factor governing the balance between its physiological role as a multifunctional scaffold protein and aggregation-related aberrations with potential significance for disease.

Mapping Sex-Specific Neurodevelopmental Alterations in Neurite Density and Morphology in a Rat Genetic Model of Psychiatric Illness

Neurite orientation dispersion and density imaging (NODDI) is an emerging magnetic resonance (MR) diffusion-weighted imaging (DWI) technique that permits non-invasive quantitative assessment of neurite density and morphology. NODDI has improved our ability to image neuronal microstructure over conventional techniques such as diffusion tensor imaging (DTI) and is particularly suited for studies of the developing brain as it can measure and characterize the dynamic changes occurring in dendrite cytoarchitecture that are critical to early brain development. Neurodevelopmental alterations to the diffusion tensor have been reported in psychiatric illness, but it remains unknown whether advanced DWI techniques such as NODDI are able to sensitively and specifically detect neurodevelopmental changes in brain microstructure beyond those provided by DTI. We show, in an extension of our previous work with a Disc1 svΔ2 rat genetic model of psychiatric illness, the enhanced sensitivity and specificity of NODDI to identify neurodevelopmental and sex-specific changes in brain microstructure that are otherwise difficult to observe with DTI and further corroborate observed changes in brain microstructure to differences in sex-specific systems-level animal behavior. Together, these findings inform the potential application and clinical translational utility of NODDI in studies of brain microstructure in psychiatric illness throughout neurodevelopment and further, the ability of advanced DWI methods such as NODDI to examine the role of biological sex and its influence on brain microstructure in psychiatric illness.

Convergent brain microstructure across multiple genetic models of schizophrenia and autism spectrum disorder: A feasibility study

Neuroimaging studies of psychiatric illness have revealed a broad spectrum of structural and functional perturbations that have been attributed in part to the complex genetic heterogeneity underpinning these disorders. These perturbations have been identified in both preclinical genetic models and in patients when compared to control populations, but recent work has also demonstrated strong evidence for genetic, molecular, and structural convergence of several psychiatric diseases. We explored potential similarities in neural microstructure in preclinical genetic models of ASD (Fmr1, Nrxn1, Pten) and schizophrenia (Disc1 svΔ2) and in age- and sex-matched control animals with diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI). Our findings demonstrate a convergence in brain microstructure across these four genetic models with both tract-based and region-of-interest based analyses, which continues to buttress an emerging understanding of converging neural microstructure in psychiatric disease.

Metabolic Changes in Synaptosomes in an Animal Model of Schizophrenia Revealed by 1H and 1H,13C NMR Spectroscopy

Synaptosomes are isolated nerve terminals that contain synaptic components, including neurotransmitters, metabolites, adhesion/fusion proteins, and nerve terminal receptors. The essential role of synaptosomes in neurotransmission has stimulated keen interest in understanding both their proteomic and metabolic composition. Mass spectrometric (MS) quantification of synaptosomes has illuminated their proteomic composition, but the determination of the metabolic composition by MS has been met with limited success. In this study, we report a proof-of-concept application of one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy for analyzing the metabolic composition of synaptosomes. We utilize this approach to compare the metabolic composition synaptosomes from a wild-type rat with that from a newly generated genetic rat model (Disc1 svΔ2), which qualitatively recapitulates clinically observed early DISC1 truncations associated with schizophrenia. This study demonstrates the feasibility of using NMR spectroscopy to identify and quantify metabolites within synaptosomal fractions.

Disrupted in Schizophrenia 1 regulates the processing of reelin in the perinatal cortex

Disrupted in Schizophrenia 1 (DISC1) is a prominent gene in mental illness research, encoding a scaffold protein known to be of importance in the developing cerebral cortex. Reelin is a critical extracellular protein for development and lamination of the prenatal cortex and which has also been independently implicated in mental illness. Regulation of reelin activity occurs through processing by the metalloproteinases ADAMTS-4 and ADAMTS-5. Through cross-breeding of heterozygous transgenic DISC1 mice with heterozygous reeler mice, which have reduced reelin, pups heterozygous for both phenotypes were generated. From these, we determine that transgenic DISC1 leads to a reduction in the processing of reelin, with implications for its downstream signalling element Dab1. An effect of DISC1 on reelin processing was confirmed in vitro, and revealed that intracellular DISC1 affects ADAMTS-4 protein, which in turn is exported and affects processing of extracellular reelin. In transgenic rat cortical cultures, an effect of DISC1 on reelin processing could also be seen specifically in early, immature neurons, but was lost in calretinin and reelin-positive mature neurons, suggesting cell-type specificity. DISC1 therefore acts upstream of reelin in the perinatal cerebral cortex in a cell type/time specific manner, leading to regulation of its activity through altered proteolytic cleavage. Thus a functional link is demonstrated between two proteins, each of independent importance for both cortical development and associated cognitive functions leading to behavioural maladaptation and mental illness.

Genetic Advance in Depressive Disorder

Major depressive disorder (MDD) and bipolar disorder (BPD) are both chronic, severe mood disorder with high misdiagnosis rate, leading to substantial health and economic burdens to patients around the world. There is a high misdiagnosis rate of bipolar depression (BD) just based on symptomology in depressed patients whose previous manic or mixed episodes have not been well recognized. Therefore, it is important for psychiatrists to identify these two major psychiatric disorders. Recently, with the accumulation of clinical sample sizes and the advances of methodology and technology, certain progress in the genetics of major depression and bipolar disorder has been made. This article reviews the candidate genes for MDD and BD, genetic variation loci, chromosome structural variation, new technologies, and new methods.

A critical review of zebrafish schizophrenia models: Time for validation?

Schizophrenia is a mental disorder that affects 1% of the population worldwide and is manifested as a broad spectrum of symptoms, from hallucinations to memory impairment. It is believed that genetic and/or environmental factors may contribute to the occurrence of this disease. Recently, the zebrafish has emerged as a valuable and attractive model for various neurological disorders including schizophrenia. In this review, we describe current pharmacological models of schizophrenia with special emphasis on providing insights into the pros and cons of using zebrafish as a behavioural model of this disease. Moreover, we highlight the advantages and utility of using zebrafish for elucidating the genetic mechanisms underlying this psychiatric disorder. We believe that the zebrafish has high potential also in the area of precision medicine and may complement the development of therapeutics, especially for pharmacoresistant patients.

Disrupted-in-schizophrenia 1 functional polymorphisms and D2 /D3 receptor availability: A [11 C]-(+)-PHNO imaging study

The disrupted-in-schizophrenia 1 (DISC1) protein has been implicated in a range of biological mechanisms underlying chronic mental disorders such as schizophrenia. Schizophrenia is associated with abnormal striatal dopamine signalling, and all antipsychotic drugs block striatal dopamine 2/3 receptors (D_2/3 Rs). Importantly, the DISC1 protein directly interacts and forms a protein complex with the dopamine D₂ receptor (D₂ R) that inhibits agonist-induced D₂ R internalisation. Moreover, animal studies have found large striatal increases in the proportion of D₂ R receptors in a high affinity state (D₂ ^high R) in DISC1 rodent models. Here, we investigated the relationship between the three most common polymorphisms altering the amino-acid sequence of the DISC1 protein (Ser704Cys (rs821616), Leu607Phe (rs6675281) and Arg264Gln (rs3738401)) and striatal D_2/3 R availability in 41 healthy human volunteers, using [¹¹ C]-(+)-PHNO positron emission tomography. We found no association between DISC1 polymorphisms and D_2/3 R availability in the striatum and D₂ R availability in the caudate and putamen. Therefore, despite a direct interaction between DISC1 and the D₂ R, none of its main functional polymorphisms impact striatal D_2/3 R binding potential, suggesting DISC1 variants act through other mechanisms.

Kinase network dysregulation in a human induced pluripotent stem cell model of DISC1 schizophrenia

Protein kinases orchestrate signal transduction pathways involved in central nervous system functions ranging from neurodevelopment to synaptic transmission and plasticity. Abnormalities in kinase-mediated signaling are involved in the pathophysiology of neurological disorders, including neuropsychiatric disorders. Here, we expand on the hypothesis that kinase networks are dysregulated in schizophrenia. We investigated changes in serine/threonine kinase activity in cortical excitatory neurons differentiated from induced pluripotent stem cells (iPSCs) from a schizophrenia patient presenting with a 4 bp mutation in the disrupted in schizophrenia 1 (DISC1) gene and a corresponding control. Using kinome peptide arrays, we demonstrate large scale abnormalities in DISC1 cells, including a global depression of serine/threonine kinase activity, and changes in activity of kinases, including AMP-activated protein kinase (AMPK), extracellular signal-regulated kinases (ERK), and thousand-and-one amino acid (TAO) kinases. Using isogenic cell lines in which the DISC1 mutation is either introduced in the control cell line, or rescued in the schizophrenia cell line, we ascribe most of these changes to a direct effect of the presence of the DISC1 mutation. Investigating the gene expression signatures downstream of the DISC1 kinase network, and mapping them on perturbagen signatures obtained from the Library of Integrated Network-based Cellular Signatures (LINCS) database, allowed us to propose novel drug targets able to reverse the DISC1 kinase dysregulation gene expression signature. Altogether, our findings provide new insight into abnormalities of kinase networks in schizophrenia and suggest possible targets for disease intervention.

A DISC1 point mutation promotes oligomerization and impairs information processing in a mouse model of schizophrenia

Disrupted-in-schizophrenia 1 (DISC1) is strongly associated with schizophrenia, but it remains elusive how the modification of the intermolecular interaction of DISC1 affects the information processing in brain. We show that a DISC1 point mutation alters intermolecular cohesiveness promoting the phase separation, and disrupts sensorimotor gating monitored by the prepulse inhibition in a mouse model of schizophrenia. Although the conformation of DISC1 partial peptide with the schizophrenia-related mutation L607F in human or the corresponding L604F in mouse was essentially indistinguishable from the wild type (WT) as long as monitored by fluorescence, circular dichroism, ultracentrifugation, dynamic light scattering and nuclear magnetic resonance, the atomic force microscopy was able to detect their morphological distinctions. The WT peptides were round and well dispersed, while mutants were inhomogeneous and disrupted to form dimer to trimer that aligned along one direction without apparent aggregate formation. Homozygous L604F mutant mice created by CRISPR exhibited the significant decrease in DISC1 level in the immunohistopathology at the hippocampal region compared to the WTs. The ratio of prepulse inhibition of the homozygous mutant mice was significantly impaired compared to WTs. Altered DISC1 distribution or function caused by aberrant intermolecular interactions may contribute to information processing characteristics in schizophrenia.

Endogenous Cell Type-Specific Disrupted in Schizophrenia 1 Interactomes Reveal Protein Networks Associated With Neurodevelopmental Disorders

BACKGROUND

Disrupted in schizophrenia 1 (DISC1) has been implicated in a number of psychiatric diseases along with neurodevelopmental phenotypes such as the proliferation and differentiation of neural progenitor cells. While there has been significant effort directed toward understanding the function of DISC1 through the determination of its protein-protein interactions within an in vitro setting, endogenous interactions involving DISC1 within a cell type-specific setting relevant to neural development remain unclear.

METHODS

Using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) genome engineering technology, we inserted an endogenous 3X-FLAG tag at the C-terminus of the canonical DISC1 gene in human induced pluripotent stem cells (iPSCs). We further differentiated these cells and used affinity purification to determine protein-protein interactions involving DISC1 in iPSC-derived neural progenitor cells and astrocytes.

RESULTS

We were able to determine 151 novel cell type-specific proteins present in DISC1 endogenous interactomes. The DISC1 interactomes can be clustered into several subcomplexes that suggest novel DISC1 cell-specific functions. In addition, the DISC1 interactome in iPSC-derived neural progenitor cells associates in a connected network containing proteins found to harbor de novo mutations in patients affected by schizophrenia and contains a subset of novel interactions that are known to harbor syndromic mutations in neurodevelopmental disorders.

CONCLUSIONS

Endogenous DISC1 interactomes within iPSC-derived human neural progenitor cells and astrocytes are able to provide context to DISC1 function in a cell type-specific setting relevant to neural development and enables the integration of psychiatric disease risk factors within a set of defined molecular functions.

Sex-specific deficits in neurite density and white matter integrity are associated with targeted disruption of exon 2 of the Disc1 gene in the rat

Diffusion tensor imaging (DTI) has provided remarkable insight into our understanding of white matter microstructure and brain connectivity across a broad spectrum of psychiatric disease. While DTI and other diffusion weighted magnetic resonance imaging (MRI) methods have clarified the axonal contribution to the disconnectivity seen in numerous psychiatric diseases, absent from these studies are quantitative indices of neurite density and orientation that are especially important features in regions of high synaptic density that would capture the synaptic contribution to the psychiatric disease state. Here we report the application of neurite orientation dispersion and density imaging (NODDI), an emerging microstructure imaging technique, to a novel Disc1 svΔ2 rat model of psychiatric illness and demonstrate the complementary and more specific indices of tissue microstructure found in NODDI than those reported by DTI. Our results demonstrate global and sex-specific changes in white matter microstructural integrity and deficits in neurite density as a consequence of the Disc1 svΔ2 genetic variation and highlight the application of NODDI and quantitative measures of neurite density and neurite dispersion in psychiatric disease.

DISC1 gene polymorphisms and the risk of schizophrenia in an Iranian population: A preliminary study

BACKGROUND

Schizophrenia, schizoaffective disorder, and bipolar illness are common psychological disorders with high heritability and variable phenotypes. The disrupted in schizophrenia 1 ( DISC1) gene, on chromosome 1q42, has an essential role in neurite outgrowth and cell signaling. The purpose of this study was to investigate the association of three single-nucleotide polymorphisms (SNPs; rs6675281, rs2255340, and rs2738864) with schizophrenia disorder. These three SNPs were chosen as they had been used in most of the previous studies.

METHODS

In a case-control study of Iranian population for the first time 778 blood samples were collected including, 402 schizophrenic patients and 376 healthy controls. Genomic DNA was extracted from peripheral blood using DNA extraction kit (BioFlux Co). The genotypes of rs6675281, rs2255340, and rs2738864 were detected by nested allele-specific multiplex polymersae chain reaction (PCR).

RESULTS

Our data revealed that the three SNPs are significantly associated with schizophrenia (rs2255349 C>T: confidence interval (CI), 2.115 to 3.268; P = 0.0000 OR: 2.629; rs2738864 C>T: CI, 1.538 to 2.339; P = 0.0000 OR: 1.897; rs6675281 C>T: CI, 2.788 to 4.662; P = 0.0009241 OR: 3.605). Through applying the expectation-maximization (EM) algorithm, we calculated the haplotype frequency, and finally performed haplotype analysis with Bonferroni correction and data preprocessing methods and the results showed rs66875281 to have the highest association.

DISCUSSION

Our findings primarily showed that DISC1 gene polymorphisms contribute to schizophrenia risk and have a significant association with this disorder among Iranian population. The strategy was found to be easy, rapid, specific, and consistent for the co-occurring detection of the DISC1 polymorphisms. We could finally confirm that the polymorphisms are related to schizophrenia studied in Iranian population.

Interactome Studies of Psychiatric Disorders

High comorbidity and complexity have precluded reliable diagnostic assessment and treatment of psychiatric disorders. Impaired molecular interactions may be relevant for underlying mechanisms of psychiatric disorders but by and large remain unknown. With the help of a number of publicly available databases and various technological tools, recent research has filled the paucity of information by generating a novel dataset of psychiatric interactomes. Different technological platforms including yeast two-hybrid screen, co-immunoprecipitation-coupled with mass spectrometry-based proteomics, and transcriptomics have been widely used in combination with cellular and molecular techniques to interrogate the psychiatric interactome. Novel molecular interactions have been identified in association with different psychiatric disorders including autism spectrum disorders, schizophrenia, bipolar disorder, and major depressive disorder. However, more extensive and sophisticated interactome research needs to be conducted to overcome the current limitations such as incomplete interactome databases and a lack of functional information among components. Ultimately, integrated psychiatric interactome databases will contribute to the implementation of biomarkers and therapeutic intervention.

Association on DISC1 SNPs with schizophrenia risk: A meta-analysis

Schizophrenia is a major psychiatric disorder with complex genetic, environmental, and psychological etiologies. Although DISC1 gene has been shown as a risk factor for schizophrenia in some reports, there is a lack of a consensus. We therefore performed separate meta-analyses aiming to assess the associations between DISC1 SNPs and schizophrenia risk. We found that SNP rs821597 is significantly associated with schizophrenia risk in terms of both allelic and genotypic distribution, while SNP rs821616 is associated with schizophrenia in terms of genotypic distribution, especially in cases above 40 years old.

The effect of the DISC1 Ser704Cys polymorphism on striatal dopamine synthesis capacity: an [18F]-DOPA PET study

Whilst the role of the Disrupted-in-Schizophrenia 1 (DISC1) gene in the aetiology of major mental illnesses is debated, the characterization of its function lends it credibility as a candidate. A key aspect of this functional characterization is the determination of the role of common non-synonymous polymorphisms on normal variation within these functions. The common allele (A) of the DISC1 single-nucleotide polymorphism (SNP) rs821616 encodes a serine (ser) at the Ser704Cys polymorphism, and has been shown to increase the phosphorylation of extracellular signal-regulated protein Kinases 1 and 2 (ERK1/2) that stimulate the phosphorylation of tyrosine hydroxylase, the rate-limiting enzyme for dopamine biosynthesis. We therefore set out to test the hypothesis that human ser (A) homozygotes would show elevated dopamine synthesis capacity compared with cysteine (cys) homozygotes and heterozygotes (TT and AT) for rs821616. [18F]-DOPA positron emission tomography (PET) was used to index striatal dopamine synthesis capacity as the influx rate constant Kicer in healthy volunteers DISC1 rs821616 ser homozygotes (N = 46) and healthy volunteers DISC1 rs821616 cys homozygotes and heterozygotes (N = 56), matched for age, gender, ethnicity and using three scanners. We found DISC1 rs821616 ser homozygotes exhibited a significantly higher striatal Kicer compared with cys homozygotes and heterozygotes (P = 0.012) explaining 6.4% of the variance (partial η2 = 0.064). Our finding is consistent with its previous association with heightened activation of ERK1/2, which stimulates tyrosine hydroxylase activity for dopamine synthesis. This could be a potential mechanism mediating risk for psychosis, lending further credibility to the fact that DISC1 is of functional interest in the aetiology of major mental illness.

Lead Neurotoxicity on Human Neuroblastoma Cell Line SH-SY5Y is Mediated via Transcription Factor EGR1/Zif268 Induced Disrupted in Scherophernia-1 Activation

Lead (Pb²⁺) is a well-known type of neurotoxin and chronic exposure to Pb²⁺ induces cognition dysfunction. In this work, the potential role of early growth response gene 1 (EGR1) in the linkage of Pb²⁺ exposure and disrupted in scherophernia-1 (DISC1) activity was investigated. Human neuroblastoma cell line SH-SY5Y was subjected to different concentrations of lead acetate (PbAc) to determine the effect of Pb²⁺ exposure on the cell viability, apoptosis, and activity of EGR1 and DISC1. Then the expression of EGR1 in SH-SY5Y cells was knocked down with specific siRNA to assess the function of EGR1 in Pb²⁺ induced activation of DISC1. The interaction between EGR1 and DISC1 was further validated with dual luciferase assay, Supershift electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP)-PCR. Administration of PbAc decreased cell viability and induced apoptosis in SH-SY5Y cells in a dose-dependent manner. Additionally, exposure to PbAc also up-regulated expression of EGR1 and DISC1 at all concentrations. Knockdown of EGR1 blocked the effect of PbAc on SH-SY5Y cells, indicating the central role of EGR1 in the function of Pb²⁺ on activity of DISC1. Based on the results of dual luciferase assay, Supershift EMSA, and ChIP-PCR, EGR1 mediated the effect of Pb²⁺ on DISC1 by directly bound to the promoter region of DISC1 gene. The current study elaborated the mechanism involved in the effect of Pb²⁺ exposure on expression of DISC1 for the first time: EGR1 activated by Pb²⁺ substitution of zinc triggered the transcription of DISC1 gene by directly binding to its promoter.

Shared effects of DISC1 disruption and elevated WNT signaling in human cerebral organoids

The development of three-dimensional culture methods has allowed for the study of developing cortical morphology in human cells. This provides a new tool to study the neurodevelopmental consequences of disease-associated mutations. Here, we study the effects of isogenic DISC1 mutation in cerebral organoids. DISC1 has been implicated in psychiatric disease based on genetic studies, including its interruption by a balanced translocation that increases the risk of major mental illness. Isogenic wild-type and DISC1-disrupted human-induced pluripotent stem cells were used to generate cerebral organoids, which were then examined for morphology and gene expression. We show that DISC1-mutant cerebral organoids display disorganized structural morphology and impaired proliferation, which is phenocopied by WNT agonism and rescued by WNT antagonism. Furthermore, there are many shared changes in gene expression with DISC1 disruption and WNT agonism, including in neural progenitor and cell fate markers, regulators of neuronal migration, and interneuron markers. These shared gene expression changes suggest mechanisms for the observed morphologic dysregulation with DISC1 disruption and points to new avenues for future studies. The shared changes in three-dimensional cerebral organoid morphology and gene expression with DISC1 interruption and WNT agonism further strengthens the link between DISC1 mutation, abnormalities in WNT signaling, and neuropsychiatric disease.

Gene polymorphisms of DISC1 is associated with schizophrenia: Evidence from a meta-analysis

BACKGROUND

Previous studies suggest an association between Disrupted in schizophrenia 1 (DISC1) polymorphisms and schizophrenia (SCZ). However, the available data are often inconsistent, regarding the difference in sample size, ethnicity, genotyping method, etc. Thus, we carried out a meta-analysis to determine whether DISC1 polymorphisms contributed susceptibility to SCZ.

METHODS

A methodical literature review was operated using the English and Chinese core electronic databases. Odds ratios (ORs) with 95% confidence intervals (CIs) were applied to determine the correlation between DISC1 gene polymorphisms and SCZ susceptibility. Subgroup analyses were carried out by stratification of ethnicity. P values were Bonferroni adjusted to account for multiple testing. Publication bias was evaluated by funnel plots, Egger's test and the trim and fill method.

RESULTS

Meta-analyses results suggested that DISC1 polymorphisms (rs821616 and rs821597) increased SCZ risk in overall populations. In subgroups of ethnicity, DISC1 polymorphisms (rs821616 and rs821597) was associated with susceptibility to SCZ among the Chinese population (for rs821616: TT+AT vs. AA: OR=1.338, 95% CI=1.124-1.592, P=0.001; T vs. A: OR=1.300, 95% CI=1.124-1.504, P<0.000; for rs821597: AA+AG vs. GG: OR=1.508, 95% CI=1.268-1.794, P<0.001; A vs. G: OR=1.345, 95% CI=1.184-1.527, P<0.001). A positive correlation was also observed between the single marker rs821616 and SCZ among the Japanese population in the recessive model (TT vs. AT+AA: OR=1.524, 95% CI=1.185-1.959, P=0.001). There was no significant relationship between other DISC1 polymorphisms (rs3738401, rs2273890, rs3738398, rs3738402, rs2492367, rs843979, rs3737597, rs4658971, rs1538979, rs1000731 and rs3738399) and SCZ.

CONCLUSIONS

DISC1 polymorphisms increased a risk of SCZ, especially in the Chinese population. In order to further corroborate our findings, large well-designed epidemiological studies are needed.

Association between variations in the disrupted in schizophrenia 1 gene and schizophrenia: A meta-analysis

Schizophrenia is a severe psychiatric disorder. Genetic and functional studies have strongly implicated the disrupted in schizophrenia 1 gene (DISC1) as a candidate susceptibility gene for schizophrenia. Moreover, recent association studies have indicated that several DISC1 single nucleotide polymorphisms (SNPs) are associated with schizophrenia. However, the association is hardly replicate in different ethnic group. Here, we performed a meta-analysis of the association between DISC1 SNPs and schizophrenia in which the samples were divided into subgroups according to ethnicity. Both rs3738401 and rs821616 showed not significantly association with schizophrenia in the Caucasian, Asian, Japanese or Han Chinese populations.

Biophysical insights from a single chain camelid antibody directed against the Disrupted-in-Schizophrenia 1 protein

Accumulating evidence suggests an important role for the Disrupted-in-Schizophrenia 1 (DISC1) protein in neurodevelopment and chronic mental illness. In particular, the C-terminal 300 amino acids of DISC1 have been found to mediate important protein-protein interactions and to harbor functionally important phosphorylation sites and disease-associated polymorphisms. However, long disordered regions and oligomer-forming subdomains have so far impeded structural analysis. VHH domains derived from camelid heavy chain only antibodies are minimal antigen binding modules with appreciable solubility and stability, which makes them well suited for the stabilizing proteins prior to structural investigation. Here, we report on the generation of a VHH domain derived from an immunized Lama glama, displaying high affinity for the human DISC1 C region (aa 691-836), and its characterization by surface plasmon resonance, size exclusion chromatography and immunological techniques. The VHH-DISC1 (C region) complex was also used for structural investigation by small angle X-ray scattering analysis. In combination with molecular modeling, these data support predictions regarding the three-dimensional fold of this DISC1 segment as well as its steric arrangement in complex with our VHH antibody.

Adolescent stress leads to glutamatergic disturbance through dopaminergic abnormalities in the prefrontal cortex of genetically vulnerable mice

BACKGROUND

Stress during the adolescent period influences postnatal maturation and behavioral patterns in adulthood. Adolescent stress-induced molecular and functional changes in neurons are the key clinical features of psychiatric disorders including schizophrenia.

OBJECTIVE

In the present study, we exposed genetically vulnerable mice to isolation stress to examine the molecular changes in the glutamatergic system involving N-methyl-d-aspartate (NMDA) receptors via dopaminergic disturbance in the prefrontal cortex (PFc).

RESULTS

We report that late adolescent stress in combination with Disrupted-in-Schizophrenia 1 (DISC1) genetic risk elicited alterations in glutamatergic neurons in the PFc, such as increased expression of glutamate transporters, decreased extracellular levels of glutamate, decreased concentration of d-serine, and impaired activation of NMDA-Ca2+/calmodulin kinase II signaling. These changes resulted in behavioral deficits in locomotor activity, forced swim, social interaction, and novelty preference tests. The glutamatergic alterations in the PFc were prevented if the animals were treated with an atypical antipsychotic drug clozapine and a dopamine D1 agonist SKF81297, which suggests that the activation of dopaminergic neurons is involved in the regulation of the glutamatergic system.

CONCLUSION

Our results suggest that adolescent stress combined with dopaminergic abnormalities in the PFc of genetically vulnerable mice induces glutamatergic disturbances, which leads to behavioral deficits in the young adult stage.

The atypical dopamine receptor agonist SKF 83959 enhances hippocampal and prefrontal cortical neuronal network activity in a rat model of cognitive dysfunction

Deficits in neuronal network synchrony in hippocampus and prefrontal cortex have been widely demonstrated in disorders of cognitive dysfunction, including schizophrenia and Alzheimer's disease. The atypical dopamine agonist SKF 83959 has been shown to increase brain-derived neurotrophic factor signalling and suppress activity of glycogen synthase kinase-3 in PFC, two processes important to learning and memory. The purpose of this study was to therefore evaluate the impact of SKF 83959 on oscillatory deficits in methylazoxymethanol acetate (MAM) rat model of schizophrenia. To achieve this, local field potentials were recorded simultaneously from the hippocampus and prefrontal cortex of anesthetized rats at 15 and 90 min following both acute and repeated administration of SKF 83959 (0.4 mg/kg). In MAM rats, but not controls, repeated SKF 83959 treatment increased signal amplitude in hippocampus and enhanced the spectral power of low frequency delta and theta oscillations in this region. In PFC, SKF 83959 increased delta, theta and gamma spectral power. Increased HIP-PFC theta coherence was also evident following acute and repeated SKF 83959. In apparent contradiction to these oscillatory effects, in MAM rats, SKF 83959 inhibited spatial learning and induced a significant increase in thigmotactic behaviour. These findings have uncovered a previously unknown role for SKF 83959 in the positive regulation of hippocampal-prefrontal cortical oscillatory network activity. As SKF 83959 is known to have affinity for a number of receptors, delineating the receptor mechanisms that mediate the positive drug effects on neuronal oscillations could have significant future implications in disorders associated with cognitive dysfunction.

Prefrontal mechanisms of comorbidity from a transdiagnostic and ontogenic perspective

Accumulating behavioral and genetic research suggests that most forms of psychopathology share common genetic and neural vulnerabilities and are manifestations of a relatively few core underlying processes. These findings support the view that comorbidity mostly arises, not from true co-occurrence of distinct disorders, but from the behavioral expression of shared vulnerability processes across the life span. The purpose of this review is to examine the role of the prefrontal cortex (PFC) in the shared vulnerability mechanisms underlying the clinical phenomena of comorbidity from a transdiagnostic and ontogenic perspective. In adopting this perspective, we suggest complex transactions between neurobiologically rooted vulnerabilities inherent in PFC circuitry and environmental factors (e.g., parenting, peers, stress, and substance use) across development converge on three key PFC-mediated processes: executive functioning, emotion regulation, and reward processing. We propose that individual differences and impairments in these PFC-mediated functions provide intermediate mechanisms for transdiagnostic symptoms and underlie behavioral tendencies that evoke and interact with environmental risk factors to further potentiate vulnerability.

The YWHAE gene confers risk to major depressive disorder in the male group of Chinese Han population

Schizophrenia and major depressive disorder are two major psychiatric illnesses that may share specific genetic risk factors to a certain extent. Increasing evidence suggests that the two disorders might be more closely related than previously considered. To investigate whether YWHAE gene plays a significant role in major depressive disorder in Han Chinese population, we recruited 1135 unrelated major depressive disorder patients (485 males, 650 females) and 989 unrelated controls (296 males, 693 females) of Chinese Han origin. Eleven common SNPs were genotyped using TaqMan® technology. In male-group, the allele and genotype frequencies of rs34041110 differed significantly between patients and control (P_allele=0.036486, OR[95%CI]: 1.249442(1.013988-1.539571); P_genotype=0.045301). Also in this group, allele and genotype frequencies of rs1532976 differed significantly (P_allele=0.013242, OR[95%CI]: 1.302007(1.056501-1.604563); genotype: P=0.039152). Haplotype-analyses showed that, in male-group, positive association with major depressive disorder was found for the A-A-C-G haplotype of rs3752826-rs2131431-rs1873827-rs12452627 (χ²=20.397, P=6.38E-06, OR[95%CI]: 7.442 [2.691-20.583]), its C-A-C-G haplotype (χ²=19.122, P=1.24E-05, OR and 95%CI: 0.402 [0.264-0.612]), its C-C-T-G haplotype (χ²=9.766, P=0.001785, OR[95%CI]: 5.654 [1.664-19.211]). In female-group, positive association was found for the A-A-C-G haplotype of rs3752826-rs2131431-rs1873827-rs12452627 (χ²=78.628, P=7.94E-19, OR[95%CI]: 50.043 [11.087-225.876]), its A-C-T-G haplotype (χ²=38.806, P=4.83E-10, OR[95%CI]: 0.053 [0.015-0.192]), the C-A-C-G haplotype (χ²=18.930, P=1.37E-05, OR[95%CI]: 0.526 [0.392-0.705]), and the C-C-T-G haplotype (χ²=38.668, P=5.18E-10, OR[95%CI]: 6.130 [3.207-11.716]). Our findings support YWHAE being a risk gene for Major Depressive Disorder in the Han Chinese population.

White matter atrophy and myelinated fiber disruption in a rat model of depression

Brain imaging and postmortem studies have indicated that white matter abnormalities may contribute to the pathology and pathogenesis of depression. However, until now, no study has quantitatively investigated white matter changes in depression in rats. The current study used the chronic unpredictable stress (CUS) model of depression. Body weight and sucrose preference test (SPT) scores were assessed weekly. Upon successfully establishing the CUS animal model, all animals were tested using the SPT and the open field test (OFT). Then, transmission electron microscopy and unbiased stereological methods were used to investigate white matter changes in the rats. Compared with the control group, the body weight and sucrose preference of the CUS rats were significantly decreased (p < .001, p < .001, respectively). In the OFT, the total time spent and the total distance traveled in the inner area by the CUS rats were significantly lower than those of the control group (p = .002, p = .001, respectively). The stereological results revealed that white matter volume, the total volume, and the total length and mean diameter of myelinated fibers in the white matter of the CUS rats were significantly decreased compared to the control rats (p = .042, p = .038, p = .035, p = .019, respectively). The results of this study suggested that white matter atrophy and disruption of myelinated fibers in the white matter may contribute to the pathophysiology underlying depression, which might provide new targets for the development of novel therapeutic interventions for depression.

The impact of Disrupted-in-Schizophrenia 1 (DISC1) on the dopaminergic system: a systematic review

Disrupted-in-Schizophrenia 1 (DISC1) is a gene known as a risk factor for mental illnesses possibly associated with dopamine impairments. DISC1 is a scaffold protein interacting with proteins involved in the dopamine system. Here we summarise the impact of DISC1 disruption on the dopamine system in animal models, considering its effects on presynaptic dopaminergic function (tyrosine hydroxylase levels, dopamine transporter levels, dopamine levels at baseline and after amphetamine administration) and postsynaptic dopaminergic function (dopamine D1 and D2 receptor levels, dopamine receptor-binding potential and locomotor activity after amphetamine administration). Our findings show that many but not all DISC1 models display (1) increased locomotion after amphetamine administration, (2) increased dopamine levels after amphetamine administration in the nucleus accumbens, and (3) inconsistent basal dopamine levels, dopamine receptor levels and binding potentials. There is also limited evidence for decreased tyrosine hydroxylase levels in the frontal cortex and increased dopamine transporter levels in the striatum but not nucleus accumbens, but these conclusions warrant further replication. The main dopaminergic findings are seen across different DISC1 models, providing convergent evidence that DISC1 has a role in regulating dopaminergic function. These results implicate dopaminergic dysregulation as a mechanism underlying the increased rate of schizophrenia seen in DISC1 variant carriers, and provide insights into how DISC1, and potentially DISC1-interacting proteins such as AKT and GSK-3, could be used as novel therapeutic targets for schizophrenia.

Primary Cilia as a Possible Link between Left-Right Asymmetry and Neurodevelopmental Diseases

Cilia have multiple functions in the development of the entire organism, and participate in the development and functioning of the central nervous system. In the last decade, studies have shown that they are implicated in the development of the visceral left-right asymmetry in different vertebrates. At the same time, some neuropsychiatric disorders, such as schizophrenia, autism, bipolar disorder, and dyslexia, are known to be associated with lateralization failure. In this review, we consider possible links in the mechanisms of determination of visceral asymmetry and brain lateralization, through cilia. We review the functions of seven genes associated with both cilia, and with neurodevelopmental diseases, keeping in mind their possible role in the establishment of the left-right brain asymmetry.

Additive sex-specific influence of common non-synonymous DISC1 variants on amygdala, basal ganglia, and white cortical surface area in healthy young adults

The disrupted-in-schizophrenia-1 (DISC1) gene is known for its role in the development of mental disorders. It is also involved in neurodevelopment, cognition, and memory. To investigate the association between DISC1 variants and brain morphology, we analyzed the influence of the three common non-synonymous polymorphisms in DISC1 on specific brain structures in healthy young adults. The volumes of brain regions were determined in 145 subjects by magnetic resonance imaging and automated analysis using FreeSurfer. Genotyping was performed by high resolution melting of amplified products. In an additive genetic model, rs6675281 (Leu607Phe), rs3738401 (Arg264Gln), and rs821616 (Ser704Cys) significantly explained the volume variance of the amygdala (p = 0.007) and the pallidum (p = 0.004). A higher cumulative portion of minor alleles was associated with larger volumes of the amygdala (p = 0.005), the pallidum (p = 0.001), the caudate (p = 0.024), and the putamen (p = 0.007). Sex-stratified analysis revealed a strong genetic effect of rs6675281 on putamen and pallidum in females but not in males and an opposite influence of rs3738401 on the white cortical surface in females compared to males. The strongest single association was found for rs821616 and the amygdala volume in male subjects (p < 0.001). No effect was detected for the nucleus accumbens. We report-to our knowledge-for the first time a significant and sex-specific influence of common DISC1 variants on volumes of the basal ganglia, the amygdala and on the cortical surface area. Our results demonstrate that the additive model of all three polymorphisms outperforms their single analysis.

Emerging roles of ARHGAP33 in intracellular trafficking of TrkB and pathophysiology of neuropsychiatric disorders

Intracellular trafficking of receptor proteins is essential for neurons to detect various extracellular factors during the formation and refinement of neural circuits. However, the precise mechanisms underlying the trafficking of neurotrophin receptors to synapses remain elusive. Here, we demonstrate that a brain-enriched sorting nexin, ARHGAP33, is a new type of regulator for the intracellular trafficking of TrkB, a high-affinity receptor for brain-derived neurotrophic factor. ARHGAP33 knockout (KO) mice exhibit reduced expression of synaptic TrkB, impaired spine development and neuropsychiatric disorder-related behavioural abnormalities. These deficits are rescued by specific pharmacological enhancement of TrkB signalling in ARHGAP33 KO mice. Mechanistically, ARHGAP33 interacts with SORT1 to cooperatively regulate TrkB trafficking. Human ARHGAP33 is associated with brain phenotypes and reduced SORT1 expression is found in patients with schizophrenia. We propose that ARHGAP33/SORT1-mediated TrkB trafficking is essential for synapse development and that the dysfunction of this mechanism may be a new molecular pathology of neuropsychiatric disorders.

The molecular mechanisms of neurotrophin receptor trafficking are only partially understood. Here the authors show that ARHGAP33 interacts with SORT1 to regulate TrkB trafficking, the dysfunction of which impairs synapse development and leads to schizophrenia-related behavioural abnormalities in mice.

Missense mutation in DISC1 C-terminal coiled-coil has GSK3β signaling and sex-dependent behavioral effects in mice

Disrupted-in-Schizophrenia 1 (DISC1) is a risk factor for schizophrenia and affective disorders. The full-length DISC1 protein consists of an N-terminal 'head' domain and a C-terminal tail domain that contains several predicted coiled-coils, structural motifs involved in protein-protein interactions. To probe the in vivo effects of missense mutation of DISC1's C-terminal tail, we tested mice carrying mutation D453G within a predicted α-helical coiled-coil region. We report that, relative to wild-type littermates, female DISC1(D453G) mice exhibited novelty-induced hyperlocomotion, an anxiogenic profile in the elevated plus-maze and open field tests, and reduced social exploration of unfamiliar mice. Male DISC1(D453G) mice displayed a deficit in passive avoidance, while neither males nor females exhibited any impairment in startle reactivity or prepulse inhibition. Whole brain homogenates showed normal levels of DISC1 protein, but decreased binding of DISC1 to GSK3β, decreased phospho-inhibition of GSK3β at serine 9, and decreased levels of β-catenin in DISC1(D453G) mice of either sex. Interrupted GSK3β signaling may thus be part of the mechanism underlying the behavioral phenotype associated with D453G, in common with the previously described N-terminal domain mutations Q31L and L100P in mice, and the schizophrenia risk-conferring variant R264Q in humans.

Working memory genetics in schizophrenia and related disorders: An RDoC perspective

Improved classification of mental disorders through neurobiological measures will require a set of traits that map to transdiagnostic subgroups of patients and align with heritable, core psychopathological processes at the center of the disorders of interest. A promising candidate is working memory (WM) function, for which deficits have been reported across multiple diagnostic entities including schizophrenia, bipolar disorder, ADHD, autism, and major depressive disorder. Here we review genetic working memory associations and their brain functional correlates from the perspective of identifying patient subgroups across conventional diagnostic boundaries, explore the utility of multimodal investigations integrating functional information at the neural systems level and explore potential limitations as well as future directions for research.

Altered ERK1/2 Signaling in the Brain of Learned Helpless Rats: Relevance in Vulnerability to Developing Stress-Induced Depression

Extracellular signal-regulated kinase 1/2- (ERK1/2-) mediated cellular signaling plays a major role in synaptic and structural plasticity. Although ERK1/2 signaling has been shown to be involved in stress and depression, whether vulnerability to develop depression is associated with abnormalities in ERK1/2 signaling is not clearly known. The present study examined ERK1/2 signaling in frontal cortex and hippocampus of rats that showed vulnerability (learned helplessness, (LH)) or resiliency (non-learned helplessness, (non-LH)) to developing stress-induced depression. In frontal cortex and hippocampus of LH rats, we found that mRNA and protein expressions of ERK1 and ERK2 were significantly reduced, which was associated with their reduced activation and phosphorylation in cytosolic and nuclear fractions, where ERK1 and ERK2 target their substrates. In addition, ERK1/2-mediated catalytic activities and phosphorylation of downstream substrates RSK1 (cytosolic and nuclear) and MSK1 (nuclear) were also lower in the frontal cortex and hippocampus of LH rats without any change in their mRNA or protein expression. None of these changes were evident in non-LH rats. Our study indicates that ERK1/2 signaling is differentially regulated in LH and non-LH rats and suggests that abnormalities in ERK1/2 signaling may be crucial in the vulnerability to developing depression.

Common mechanisms of excitatory and inhibitory imbalance in schizophrenia and autism spectrum disorders

Autism Spectrum Disorders (ASD) and Schizophrenia (SCZ) are cognitive disorders with complex genetic architectures but overlapping behavioral phenotypes, which suggests common pathway perturbations. Multiple lines of evidence implicate imbalances in excitatory and inhibitory activity (E/I imbalance) as a shared pathophysiological mechanism. Thus, understanding the molecular underpinnings of E/I imbalance may provide essential insight into the etiology of these disorders and may uncover novel targets for future drug discovery. Here, we review key genetic, physiological, neuropathological, functional, and pathway studies that suggest alterations to excitatory/inhibitory circuits are keys to ASD and SCZ pathogenesis.