Disrupted In Schizophrenia 1 Protein Research Articles

Disrupted-in-schizophrenia 1 protein aggregates in cerebrospinal fluid are elevated in patients with first-episode psychosis.

The disrupted-in-schizophrenia 1 (DISC1) protein is a key regulator at the intersection of major signaling pathways relevant for adaptive behavior. It is prone to posttranslational changes such as misassembly and aggregation but the significance of such transformations for human mental illness has remained unclear. We aimed to demonstrate the occurrence of DISC1 protein aggregates in patients with first-episode psychosis (FEP). Cerebrospinal fluid samples of patients with FEP (n = 50) and matched healthy controls (HCs; n = 47) were measured by the highly sensitive surface-based fluorescence intensity distribution analysis technology that enables single aggregate detection. We demonstrate that DISC1 protein aggregates are increased in cerebrospinal fluid samples of patients with FEP versus HCs. The concentration was in the low femtomolar range. No correlations were found with specific symptom levels, but the difference was particularly significant in the subset of patients with the diagnoses schizophrenia, unspecified (DSM-IV 295.9) or schizoaffective disorder (DSM-IV 295.70) at 18-month follow-up. DISC1 protein aggregate levels did not significantly change within the 18-month observation interval and were on average higher for individuals carrying the major DISC1 rs821577 allele, before correction. The occurrence of protein aggregates in vivo in patients with psychotic disorders has not been previously reported. It underscores the significance of posttranslational modifications of proteins both as pathogenetic mechanisms and as potential diagnostic markers in these disorders.

50-kHz ultrasonic vocalizations do not signal social anhedonia in transgenic DISC1 rats.

Patients diagnosed with neuropsychiatric disorders, such as autism and schizophrenia, suffer from disorganized speech. The disrupted-in-schizophrenia 1 (DISC1) protein pathway is considered a risk factor for the development of several psychiatric disorders and plays an important role in the dysregulation of dopamine (DA), which in turn plays an important role in the regulation of ultrasonic vocalizations (USVs) in rats. Moreover, the DISC1 protein pathway has been identified as a cause of social anhedonia, that is, a decrease in the drive for social interactions. USVs transmit specific affective information to other rats, with 50-kHz calls indicating a positive affective state in rats. Dysregulation of the dopaminergic system impacts the qualitative and quantitative features of USVs, such as duration, peak frequency, and the call rate. In this study, we thus used a well-established transgenic DISC1 (tgDISC1) rat line to investigate whether the neural (decreased DA levels in the dorsal striatum, amygdala, and hippocampus (HPC)) and behavioral (social anhedonia) features of tgDISC1 rats could be manifested through the modulation of their 50-kHz USVs. Analyses of three features (call rate, duration, and peak frequency) of all 50-kHz revealed no significant differences between groups, suggesting decreased DA levels in the dorsal striatum and amygdala, and HPC may affect social interaction but leave 50-kHz USV production intact.

Disrupted-in-schizophrenia 1 Protein Misassembly Impairs Cognitive Flexibility and Social Behaviors in a Transgenic Rat Model

Alterations in cognitive functions, social behaviors and stress reactions are commonly diagnosed in chronic mental illnesses (CMI). Animal models expressing mutant genes associated to CMI represent either rare mutations or those contributing only minimally to genetic risk. Non-genetic causes of CMI can be modeled by disturbing downstream signaling pathways, for example by inducing protein misassembly or aggregation. The Disrupted-in-Schizophrenia 1 (DISC1) gene was identified to be disrupted and thereby haploinsufficient in a large pedigree where it was associated with CMI. In a subset of CMI patients, the DISC1 protein misassembles to an insoluble protein. This has been modeled in a rat (tgDISC1 rat) where the full-length, non mutant human transgene was overexpressed and cognitive impairments were observed. Here, we investigated the scope of effects of DISC1 protein misassembly by investigating spatial memory, social behavior and stress resilience. In water maze tasks, the tgDISC1 rats showed intact spatial learning and memory, but were deficient in flexible adaptation to spatial reversal learning compared to littermate controls. They also displayed less social interaction. Additionally, there was a trend towards increased corticosterone levels after restraint stress in the tgDISC1 rats. Our findings suggest that DISC1 protein misassembly leads to disturbances of cognitive flexibility and social behaviors, and might also be involved in stress sensitization. Since the observed behavioral features resemble symptoms of CMI, the tgDISC1 rat may be a valuable model for the investigation of cognitive, social and – possibly – also stress-related symptoms of major mental illnesses.

Conformational heterogeneity coupled with \u03b2-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 DISC1Δ22aa 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.

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 (D2/3 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 (D2high 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 D2/3 R availability in 41 healthy human volunteers, using [11 C]-(+)-PHNO positron emission tomography. We found no association between DISC1 polymorphisms and D2/3 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 D2/3 R binding potential, suggesting DISC1 variants act through other mechanisms.

Dysregulation of a specific immune-related network of genes biologically defines a subset of schizophrenia

Currently, the clinical diagnosis of schizophrenia relies solely on self-reporting and clinical interview, and likely comprises heterogeneous biological subsets. Such subsets may be defined by an underlying biology leading to solid biomarkers. A transgenic rat model modestly overexpressing the full-length, non-mutant Disrupted-in-Schizophrenia 1 (DISC1) protein (tgDISC1 rat) was generated that defines such a subset, inspired by our previous identification of insoluble DISC1 protein in post mortem brains from patients with chronic mental illness. Besides specific phenotypes such as DISC1 protein pathology, abnormal dopamine homeostasis, and changes in neuroanatomy and behavior, this animal model also shows subtle disturbances in overarching signaling pathways relevant for schizophrenia. In a reverse-translational approach, assuming that both the animal model and a patient subset share common disturbed signaling pathways, we identified differentially expressed transcripts from peripheral blood mononuclear cells of tgDISC1 rats that revealed an interconnected set of dysregulated genes, led by decreased expression of regulator of G-protein signaling 1 (RGS1), chemokine (C–C) ligand 4 (CCL4), and other immune-related transcripts enriched in T-cell and macrophage signaling and converging in one module after weighted gene correlation network analysis. Testing expression of this gene network in two independent cohorts of patients with schizophrenia versus healthy controls (n = 16/50 and n = 54/45) demonstrated similar expression changes. The two top markers RGS1 and CCL4 defined a subset of 27% of patients with 97% specificity. Thus, analogous aberrant signaling pathways can be identified by a blood test in an animal model and a corresponding schizophrenia patient subset, suggesting that in this animal model tailored pharmacotherapies for this patient subset could be achieved.

Disrupted-in-Schizophrenia 1 (DISC1) Overexpression and Juvenile Immune Activation Cause Sex-Specific Schizophrenia-Related Psychopathology in Rats.

Synaptic pruning is a critical refinement step during neurodevelopment, and schizophrenia has been associated with overpruning of cortical dendritic spines. Both human studies and animal models implicate disrupted-in-schizophrenia 1 (DISC1) gene as a strong susceptibility factor for schizophrenia. Accumulating evidence supports the involvement of DISC1 protein in the modulation of synaptic elimination during critical periods of neurodevelopment and of dopamine D2-receptor-mediated signaling during adulthood. In many species, synaptic pruning occurs during juvenile and adolescent periods and is mediated by microglia, which can be over-activated by an immune challenge, giving rise to overpruning. Therefore, we sought to investigate possible interactions between a transgenic DISC1 model (tgDISC1) and juvenile immune activation (JIA) by the bacterial cell wall endotoxin lipopolysaccharide on the induction of schizophrenia-related behavioral and neurochemical disruptions in adult female and male rats. We examined possible behavioral aberrations along three major symptom dimensions of schizophrenia including psychosis, social and emotional disruptions, and cognitive impairments. We detected significant gene–environment interactions in the amphetamine-induced locomotion in female animals and in the amphetamine-induced anxiety in male animals. Surprisingly, gene–environment interactions improved social memory in both male and female animals. JIA alone disrupted spatial memory and recognition memory, but only in male animals. DISC1 overexpression alone induced an improvement in sensorimotor gating, but only in female animals. Our neurochemical analyses detected sex- and manipulation-dependent changes in the postmortem monoamine content of animals. Taken together, we here report sex-specific effects of environment and genotype as well as their interaction on behavioral phenotypes and neurochemical profiles relevant for schizophrenia.

Disrupted-in-schizophrenia 1 overexpression disrupts hippocampal coding and oscillatory synchronization.

Aberrant proteostasis of protein aggregation may lead to behavior disorders including chronic mental illnesses (CMI). Furthermore, the neuronal activity alterations that underlie CMI are not well understood. We recorded the local field potential and single‐unit activity of the hippocampal CA1 region in vivo in rats transgenically overexpressing the Disrupted‐in‐Schizophrenia 1 (DISC1) gene (tgDISC1), modeling sporadic CMI. These tgDISC1 rats have previously been shown to exhibit DISC1 protein aggregation, disturbances in the dopaminergic system and attention‐related deficits. Recordings were performed during exploration of familiar and novel open field environments and during sleep, allowing investigation of neuronal abnormalities in unconstrained behavior. Compared to controls, tgDISC1 place cells exhibited smaller place fields and decreased speed‐modulation of their firing rates, demonstrating altered spatial coding and deficits in encoding location‐independent sensory inputs. Oscillation analyses showed that tgDISC1 pyramidal neurons had higher theta phase locking strength during novelty, limiting their phase coding ability. However, their mean theta phases were more variable at the population level, reducing oscillatory network synchronization. Finally, tgDISC1 pyramidal neurons showed a lack of novelty‐induced shift in their preferred theta and gamma firing phases, indicating deficits in coding of novel environments with oscillatory firing. By combining single cell and neuronal population analyses, we link DISC1 protein pathology with abnormal hippocampal neural coding and network synchrony, and thereby gain a more comprehensive understanding of CMI mechanisms.

SA92 - BIOINFORMATICS ANALYSIS OF RARE AMINO ACID SUBSTITUTIONS IN THE DISC1 INTERACTOME IMPLICATED IN SCHIZOPHRENIA

Background Disrupted In Schizophrenia 1 (DISC1) gene is a well-researched target for developing psychiatric disorders including schizophrenia, bipolar disorder and major depression. DISC1 protein directly interacts with a large set of proteins, so-called DISC1 Interactome, that are involved in brain development and neuronal signaling. Recent exome sequencing projects showed that coding variants with low allele frequency have large effects on the risk for developing schizophrenia, which indicates that rare mutations account for much of the missing heritability in the development of schizophrenia. Methods In the presented study, we applied bioinformatics approaches to analyse the effects of rare amino acid substitutions in the DISC1 Interactome on protein structure and function from public databases. We applied sequence-based machine learning methods to predict the effects of the rare disease-causing mutations on protein function, protein stability and post translational modification. In addition, we carried out structure-based modelling methods to analyse the effects of rare mutations on protein stability and protein-protein interaction. Results We collected 6,254 non-synonymous coding mutations reported in the 1000 Genomes Project located in 104 DISC1 Interactome genes from dbNSFP. Of the 6,254 variants, 5,929 coding mutations (95%) are rare amino acid substitutions with a minor allele frequency less than 1%. We observed that the distributions of damaging mutations are found to be higher in rare mutations than those in common mutations in the DISC1 Interactome. Some amino acid substitutions may be involved in post translational modifications such as phosphorylation and sumoylation. We showed that the rare missense mutations could significantly affect the protein structures, which result in the changes on protein stability and protein-protein interaction. Discussion The bioinformatics analysis improves our understanding of the roles of rare amino acid substitutions in the DISC1 interactome genes in susceptibility to schizophrenia. The findings can provide useful information to estimate the functional effects of rare DISC1 Interactome mutations on protein function and structure, which offer the targets for developing more precise treatments and medications for schizophrenia patients.

Mechanisms underlying the role of DISC1 in synaptic plasticity.

Disrupted in schizophrenia 1 (DISC1) is an important hub protein, forming multimeric complexes by self‐association and interacting with a large number of synaptic and cytoskeletal molecules. The synaptic location of DISC1 in the adult brain suggests a role in synaptic plasticity, and indeed, a number of studies have discovered synaptic plasticity impairments in a variety of different DISC1 mutants. This review explores the possibility that DISC1 is an important molecule for organizing proteins involved in synaptic plasticity and examines why mutations in DISC1 impair plasticity. It concentrates on DISC1's role in interacting with synaptic proteins, controlling dendritic structure and cellular trafficking of mRNA, synaptic vesicles and mitochondria. N‐terminal directed mutations appear to impair synaptic plasticity through interactions with phosphodiesterase 4B (PDE4B) and hence protein kinase A (PKA)/GluA1 and PKA/cAMP response element‐binding protein (CREB) signalling pathways, and affect spine structure through interactions with kalirin 7 (Kal‐7) and Rac1. C‐terminal directed mutations also impair plasticity possibly through altered interactions with lissencephaly protein 1 (LIS1) and nuclear distribution protein nudE‐like 1 (NDEL1), thereby affecting developmental processes such as dendritic structure and spine maturation. Many of the same molecules involved in DISC1's cytoskeletal interactions are also involved in intracellular trafficking, raising the possibility that impairments in intracellular trafficking affect cytoskeletal development and vice versa. While the multiplicity of DISC1 protein interactions makes it difficult to pinpoint a single causal signalling pathway, we suggest that the immediate‐term effects of N‐terminal influences on GluA1, Rac1 and CREB, coupled with the developmental effects of C‐terminal influences on trafficking and the cytoskeleton make up the two main branches of DISC1's effect on synaptic plasticity and dendritic spine stability.

TAR DNA-Binding Protein 43 and Disrupted in Schizophrenia 1 Coaggregation Disrupts Dendritic Local Translation and Mental Function in Frontotemporal Lobar Degeneration

BackgroundNeurodegenerative diseases involving protein aggregation often accompany psychiatric symptoms. Frontotemporal lobar degeneration (FTLD) associated with TAR DNA-binding protein 43 (TDP-43) aggregation is characterized by progressive neuronal atrophy in frontal and temporal lobes of cerebral cortex. Furthermore, patients with FTLD display mental dysfunction in multiple behavioral dimensions. Nevertheless, their molecular origin for psychiatric symptoms remains unclear. MethodsIn FTLD neurons and mouse models with TDP-43 aggregates, we examined coaggregation between TDP-43 and disrupted in schizophrenia 1 (DISC1), a key player in the pathology of mental conditions and its effects on local translation in dendrites and psychiatric behaviors. The protein coaggregation and the expression level of synaptic proteins were also investigated with postmortem brains from patients with FTLD (n = 6). ResultsWe found cytosolic TDP-43/DISC1 coaggregates in brains of both FTLD mouse model and patients with FTLD. At the mechanistic levels, the TDP-43/DISC1 coaggregates disrupted the activity-dependent dendritic local translation through impairment of translation initiation and, in turn, reduced synaptic protein expression. Behavioral deficits detected in FTLD model mice were ameliorated by exogenous DISC1 expression. ConclusionsOur findings reveal a novel role of the aggregate-prone TDP-43/DISC1 protein complex in regulating local translation, which affects aberrant behaviors relevant to multiple psychiatric dimensions.

P.1.016 - Molecular linking of influenza infection to cellular pathology of protein misassembly: the case of Disrupted-in-Schizophrenia 1 (DISC1)

Chronic mental illnesses such as schizophrenia or recurrent affective disorders are heterogeneous in their biological causes behind the clinical, syndromatic diagnosis. Viral infection has been linked to chronic mental illnesses both by direct mechanisms and indirect mechanisms through immune stimulation. For example, studies showed that intrauterine influenza infection could be a risk factor for chronic mental illness [1]. It is also established that viral infection can lead to a change in proteostasis impairing regulatory protein networks and leading to disease. The most dramatic consequences of disrupted proteostasis are the so-called protein misfolding diseases that show as a phenotypical hallmark, microscopically visible deposits of one or several proteins, and cell degeneration. More subtle forms of proteostatic imbalance exist where protein deposits are not microscopically visible and the neurons do not die but remain functionally impaired, for example in some forms of chronic mental illness such as schizophrenia [2]. We previously reported insoluble Disrupted-in-schizophrenia 1 (DISC1) protein in a subpopulation of patients with chronic mental illness [3]. This gene/protein is involved in vulnerability to chronic mental disorders, and was discovered mutant and segregating in a large Scottish pedigree with a chromosomal translocation leading to a 3′ truncation of the gene [4]. Subsequent genetic association studies in multiple populations of different ethnicities also support the involvement of this protein in mental illness. For the present study, our hypothesis was that influenza infection could cause significant long-term impairments of specific proteostatic pathways leading to aggregated DISC1 protein in chronic mental illness patients [5]. Neuroblastoma cell lines expressing inducible full-length, non-mutant DISC1 protein were infected with WSN33 influenza (H1N1 strain). The effect of viral infection was investigated by immunocytochemistry, biochemical and functional assays. Furthermore, infected mice with WSN33 influenza where investigated for insoluble DISC1 deposits by immunohistochemistry. Antiviral drugs were tested in order to reverse the influenza-induced DISC1 aggregates. Influenza infection of cell lines induced DISC1 misassembly but not misassembly of the protein TDP43 known to be mislocalized in ALS, but not in mental illness or influenza, and therefore serving as a control for specificity of DISC1 mis-assembly upon influenza infection in cellular models. Appearance of DISC1 deposits was dependent on infectious influenza virus titer, and the infection time. Functional consequences of influenza-induced DISC1 misassembly will be reported, as well as our investigations of influenza-infected mice that are still ongoing. We conclude that influenza infection leads to a very specific proteostatic change, including the misassembly of DISC1, which has functional consequences for dopamine homeostasis. Thus a selective reprogramming of cellular homeostasis, as measured by proteostasis, may be a novel molecular mechanism by which influenza infection can lead to brain disease.

Quantitative Proteomics of Synaptosomal Fractions in a Rat Overexpressing Human DISC1 Gene Indicates Profound Synaptic Dysregulation in the Dorsal Striatum.

Disrupted-in-schizophrenia 1 (DISC1) is a key protein involved in behavioral processes and various mental disorders, including schizophrenia and major depression. A transgenic rat overexpressing non-mutant human DISC1, modeling aberrant proteostasis of the DISC1 protein, displays behavioral, biochemical and anatomical deficits consistent with aspects of mental disorders, including changes in the dorsal striatum, an anatomical region critical in the development of behavioral disorders. Herein, dorsal striatum of 10 transgenic DISC1 (tgDISC1) and 10 wild type (WT) littermate control rats was used for synaptosomal preparations and for performing liquid chromatography-tandem mass spectrometry (LC-MS)-based quantitative proteomics, using isobaric labeling (TMT10plex). Functional enrichment analysis was generated from proteins with level changes. The increase in DISC1 expression leads to changes in proteins and synaptic-associated processes including membrane trafficking, ion transport, synaptic organization and neurodevelopment. Canonical pathway analysis assigned proteins with level changes to actin cytoskeleton, Gαq, Rho family GTPase and Rho GDI, axonal guidance, ephrin receptor and dopamine-DARPP32 feedback in cAMP signaling. DISC1-regulated proteins proposed in the current study are also highly associated with neurodevelopmental and mental disorders. Bioinformatics analyses from the current study predicted that the following biological processes may be activated by overexpression of DISC1, i.e., regulation of cell quantities, neuronal and axonal extension and long term potentiation. Our findings demonstrate that the effects of overexpression of non-mutant DISC1 or its misassembly has profound consequences on protein networks essential for behavioral control. These results are also relevant for the interpretation of previous as well as for the design of future studies on DISC1.

Expression Alteration of Disrupted in Schizophrenia 1 (DISC1) Gene, a Potential Peripheral Marker for Schizophrenia and Paranoid Personality Disorder

Introduction: Schizophrenia (SCZ) is a major psychiatric disorder with unclear etiology or biological diagnosis. Paranoid Personality Disorder (PPD) is a type A personality disorder characterized by paranoia and generalized mistrust. Disrupted in schizophrenia 1 (DISC1) is a gene located on human chromosome 1 that is involved in neurodevelopment of brain. Variations and translocations in this gene were found associated with schizophrenia and other psychiatric disorders. Present study aimed to evaluate the expression alteration of DISC1 gene in peripheral blood of SCZ and PPD patients and its correlation with clinical features. Material and methods: Study was included 300 SCZ, 300 PPD and 300 non-psychiatric individuals. Total blood was collected and expression level of DISC1 evaluated by using quantitative Real time PCR SYBR green. Lymphocyte DISC1 protein levels in all subjects were examined. Also, to assess psychiatric symptoms severity, Positive and Negative Syndrome Scale (PANSS) was obtained from SCZ and PPD patients. For analysis of executive functions abilities, Wisconsin Card Sorting Test (WCST) had been conducted from all subjects. Results: Findings showed significant DISC1 gene down expression in SCZ and PPD patients vs. non-psychiatrics. DISC1 protein levels were significantly decreased in SCZ and PPD vs. non-psychiatrics. Also in SCZ patients, general and negative symptoms score were associated with down regulation of DISC1 mRNA level. Executive functions deficiency had detected in SCZ and PPD and correlations were found between decrease in WSCT correct response and down expression of DISC1 in SCZ and PPD patients. Discussion and conclusion: Results presented DISC1 as potential peripheral marker for schizophrenia as well as paranoid personality disorder. Correlation between DISC1 mRNA level reduction and severity of general and negative symptoms in one side and executive functions abnormalities in the other side may support the neurodevelopment hypothesis about pathophysiology of schizophrenia and related personality disorder especially paranoid personality disorder.

Functional Proteomics Backed by Genetics and Reverse Genetic Engineering: A Novel Successful Approach to Identify Schizophrenia Subsets

BackgroundDisruption of proteostasis is a common cellular phenotype after a gentic or exogenous lesion of postmitotic neurons. In the most extreme examples, the neurodegenerative diseases, proteostasis disturbance leads to microscopically visible protein deposits. However, it is reasonable to assume that also in other chronic brain conditions, for example mental illnesses like residual schizophrenia or chronic depression, proteostasis occurs, even though clearly not accompanied by massive neuronal loss.The hypothesis of my laboratory is therefore to investigate the dsturbance of proteostasis in the context of chronic mental illnesses like schizphrenia, exemlified by the occurrence of protein pathology, ie. proteins insoluble in ionic detergents. MethodsPost mortem brains from patients with schizophrenia, bipolar disorder, depression or healthy controls were obtained from the Stanley Research Foundation (Consortium collection; n = 60), and the insoluble proteome purified by biochemical fractionation which involves several ultracentrifugation steps, the last in cold ionic detergent. The insoluble proteome of each patient was then either immunoblotted for candidate genes or pooled by diagnosis (n = 15) and injected into mice for the generation of monoclonal antibodies that would selectively recognize only schizophrenia brains but not healthy brain (epitope discovery); epitopes of such antibodies were determined on protein arrays. Finally, we also performed proteomics of the insoluble proteome by LC-MS/MS. For positive hits, genetic studies were performed to gather independent evidence. ResultsFor the rare candidate protein Disrupted-in-Schizophrenia 1 (DISC1), we could show insolubility in a subset of patients with mental illness crossing clinical diagnoses. When we modeled in a novel transgenic rat modestly overexpressing human full length DISC1, we observed disruption of dopamine homeostasis with amphetamine hypersensitivity, aberrant dopamine reuptake (Trossbach et al., 2016, Molecular Psychiatry), and aberrant dopamine as well as interneurron neuroanatomy, validating the functional notion of DISC1 protein pathology for chronic mental illness. Using epitope discovery we identified two candidate proteins, CRMP1 and TRIOBP1 as aggregated in subsets of cases with chronic mental illness. Systematic proteomics of the insoluble proteome of schizophrenia yielded more novel candidates like NKCC1 that are currently validated. DiscussionProtein pathology is a novel way of classifying chronic mental illnesses such as schizophrenia, complementing genetic analyses. Specific signatures of insoluble proteins correspond to a disease-specific failure in proteostasis. More specifically, insoluble DISC1 assemblies seem to regulate dopamine homeostasis, a brain central metabolic disturbance during psychosis

Interaction between DISC1 and CHL1 in regulation of neurite outgrowth

Disrupted-in-schizophrenia 1 (DISC1), a gene susceptible for major mental illnesses, including schizophrenia, plays multiple roles in neural development, including neuronal proliferation, maturation, migration and neurite outgrowth. DISC1 regulates neurite length via interaction with several intracellular proteins, such as NDEL1, FEZ1 and dysbindin. However, the signal transduction mechanism upstream of DISC1 in regulating neurite outgrowth remains to be elucidated. Here we show that DISC1 interacts with the intracellular domain of close homolog of L1 (CHL1), a member of the L1 family of neural cell adhesion molecules. DISC1 and CHL1 proteins co-localize in growth cones of cortical neurons. Moreover, in neurite outgrowth assay, CHL1 rescues the inhibitory effect of DISC1 on the initial phase of neurite outgrowth. Considering the fact that CHL1 also plays crucial roles in neural development, and its coding gene is associated with schizophrenia, our findings indicate that DISC1 and CHL1 may engage in physical and functional interaction in neural development, supporting the notion that DISC1 regulates neurite outgrowth with a receptor belonging to the neural cell adhesion molecules, and disruption of such interaction may contribute to increased risk for schizophrenia.

Misassembly of full-length Disrupted-in-Schizophrenia 1 protein is linked to altered dopamine homeostasis and behavioral deficits.

Disrupted-in-schizophrenia 1 (DISC1) is a mental illness gene first identified in a Scottish pedigree. So far, DISC1-dependent phenotypes in animal models have been confined to expressing mutant DISC1. Here we investigated how pathology of full-length DISC1 protein could be a major mechanism in sporadic mental illness. We demonstrate that a novel transgenic rat model, modestly overexpressing the full-length DISC1 transgene, showed phenotypes consistent with a significant role of DISC1 misassembly in mental illness. The tgDISC1 rat displayed mainly perinuclear DISC1 aggregates in neurons. Furthermore, the tgDISC1 rat showed a robust signature of behavioral phenotypes that includes amphetamine supersensitivity, hyperexploratory behavior and rotarod deficits, all pointing to changes in dopamine (DA) neurotransmission. To understand the etiology of the behavioral deficits, we undertook a series of molecular studies in the dorsal striatum of tgDISC1 rats. We observed an 80% increase in high-affinity DA D2 receptors, an increased translocation of the dopamine transporter to the plasma membrane and a corresponding increase in DA inflow as observed by cyclic voltammetry. A reciprocal relationship between DISC1 protein assembly and DA homeostasis was corroborated by in vitro studies. Elevated cytosolic dopamine caused an increase in DISC1 multimerization, insolubility and complexing with the dopamine transporter, suggesting a physiological mechanism linking DISC1 assembly and dopamine homeostasis. DISC1 protein pathology and its interaction with dopamine homeostasis is a novel cellular mechanism that is relevant for behavioral control and may have a role in mental illness.

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 DISC1D453G 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 DISC1D453G 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 DISC1D453G 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.

DISC1 Protein Regulates γ-Aminobutyric Acid, Type A (GABAA) Receptor Trafficking and Inhibitory Synaptic Transmission in Cortical Neurons

Association studies have suggested that Disrupted-in-Schizophrenia 1 (DISC1) confers a genetic risk at the level of endophenotypes that underlies many major mental disorders. Despite the progress in understanding the significance of DISC1 at neural development, the mechanisms underlying DISC1 regulation of synaptic functions remain elusive. Because alterations in the cortical GABA system have been strongly linked to the pathophysiology of schizophrenia, one potential target of DISC1 that is critically involved in the regulation of cognition and emotion is the GABAA receptor (GABAAR). We found that cellular knockdown of DISC1 significantly reduced GABAAR-mediated synaptic and whole-cell current, whereas overexpression of wild-type DISC1, but not the C-terminal-truncated DISC1 (a schizophrenia-related mutant), significantly increased GABAAR currents in pyramidal neurons of the prefrontal cortex. These effects were accompanied by DISC1-induced changes in surface GABAAR expression. Moreover, the regulation of GABAARs by DISC1 knockdown or overexpression depends on the microtubule motor protein kinesin 1 (KIF5). Our results suggest that DISC1 exerts an important effect on GABAergic inhibitory transmission by regulating KIF5/microtubule-based GABAAR trafficking in the cortex. The knowledge gained from this study would shed light on how DISC1 and the GABA system are linked mechanistically and how their interactions are critical for maintaining a normal mental state.

Increased density of DISC1-immunoreactive oligodendroglial cells in fronto-parietal white matter of patients with paranoid schizophrenia.

Profound white matter abnormalities have repeatedly been described in schizophrenia, which involve the altered expression of numerous oligodendrocyte-associated genes. Transcripts of the disrupted-in-schizophrenia 1 (DISC1) gene, a key susceptibility factor in schizophrenia, have recently been shown to be expressed by oligodendroglial cells and to negatively regulate oligodendrocyte differentiation and maturation. To learn more about the putative role(s) of oligodendroglia-associated DISC1 in schizophrenia, we analyzed the density of DISC1-immunoreactive oligodendrocytes in the fronto-parietal white matter in postmortem brains of patients with schizophrenia. Compared with controls (N=12) and cases with undifferentiated/residual schizophrenia (N=6), there was a significantly increased density of DISC1-expressing glial cells in paranoid schizophrenia (N=12), which unlikely resulted from neuroleptic treatment. Pathophysiologically, over-expression of DISC1 protein(s) in white matter oligodendrocytes might add to the reduced levels of two myelin markers, 2',3'-cyclic-nucleotide 3'-phosphodiesterase and myelin basic protein in schizophrenia. Moreover, it might significantly contribute to cell cycle abnormalities as well as to deficits in oligodendroglial cell differentiation and maturation found in schizophrenia.