Hyperactivation of midbrain dopaminergic system in schizophrenia could be attributed to the down-regulation of dysbindin

Dysbindin-1 Mutation Alters Prefrontal Cortex Extracellular Glutamate and Dopamine In Vivo

Elevated risk for schizophrenia is associated with a variation in the DTNBP1 gene encoding dysbindin-1, which may underpin cognitive impairments in this prevalent neuropsychiatric disorder. The cognitive symptoms of schizophrenia involve anomalies in glutamate and dopamine signaling, particularly within the prefrontal cortex (PFC). Indeed, mice with Dtnbp1 mutations exhibit spatial and working memory deficits that are associated with deficits in glutamate release and NMDA receptor function as determined by slice electrophysiology. The present study extended the results from ex vivo approaches by examining how the Dtnbp1 mutation impacts high K+- and NMDA receptor-evoked glutamate release within the PFC using in vivo microdialysis procedures. Dntbp1 mutant mice are also reported to exhibit blunted K+-evoked dopamine release within the PFC. Thus, we examined also K+- and NMDA-evoked dopamine release within this region. Perfusion of high-concentration K+ or NMDA solutions increased the PFC levels of both dopamine and glutamate in wild-type (WT) but not in Dtnbp1 mutants (MUT), whereas mice heterozygous for the Dtnbp1 mutation (HET) exhibited blunted K+-evoked dopamine release. No net-flux microdialysis procedures confirmed elevated basal extracellular content of both glutamate and dopamine within the PFC of HET and MUT mice. These in vivo microdialysis results corroborate prior indications that Dtnbp1 mutations perturb evoked dopamine and glutamate release within the PFC, provide in vivo evidence for impaired NMDA receptor function within the PFC, and suggest that these neurochemical anomalies may be related to abnormally elevated basal neurotransmitter content.

Loss of dysbindin-1 in excitatory neurons in mice impacts NMDAR-dependent behaviors, neuronal morphology and synaptic transmission in the ventral hippocampus

Dysbindin-1, a protein encoded by the schizophrenia susceptibility gene DTNBP1, is reduced in the hippocampus of schizophrenia patients. It is expressed in various cellular populations of the brain and implicated in dopaminergic and glutamatergic transmission. To investigate the impact of reduced dysbindin-1 in excitatory cells on hippocampal-associated behaviors and synaptic transmission, we developed a conditional knockout mouse model with deletion of dysbindin-1 gene in CaMKIIα expressing cells. We found that dysbindin-1 reduction in CaMKII expressing cells resulted in impaired spatial and social memories, and attenuation of the effects of glutamate N-methyl-d-asparate receptor (NMDAR) antagonist MK801 on locomotor activity and prepulse inhibition of startle (PPI). Dysbindin-1 deficiency in CaMKII expressing cells also resulted in reduced protein levels of NMDAR subunit GluN1 and GluN2B. These changes were associated with increased expression of immature dendritic spines in basiliar dendrites and abnormalities in excitatory synaptic transmission in the ventral hippocampus. These results highlight the functional relevance of dysbindin-1 in excitatory cells and its implication in schizophrenia-related pathologies.

Mice with dopaminergic neuron-specific deletion of DTNBP-1 gene show blunted nucleus accumbens dopamine release and associated behaviors

Reduced expression of a schizophrenia-associated gene Dystrobrevin Binding Protein 1 (DTNBP1) and its protein product dysbindin-1, has been reported in the brains of schizophrenia patients. DTNBP1-null mutant Sdy (Sandy) mice exhibit several behavioral features relevant to schizophrenia. Changes in dopaminergic as well as glutamatergic and GABAergic neurotransmission in cortico-limbic regions have been reported in Sdy mice. Since dysbindin-1 is expressed in multiple brain regions, it is not known whether dopamine (DA) changes observed in Sdy null mutants are due to dysbindin-1 deficiency in DAergic neurons specifically. Here, using a mouse line with conditional knockout (cKO) of DTNBP1 in DA neurons, we studied the effects of dysbindin-1 deficiency on DA release and DA-dependent behaviors. Spontaneous locomotor activity of cKO mice in novel environment was significantly reduced initially but was comparable at later time points with littermate controls. However, the locomotion-enhancing effect of a low dose of d-amphetamine (d-AMPH; 2.5 mg/kg, ip) was significantly attenuated in the cKO mice suggesting a dampened mesolimbic DA transmission. Similarly, the prepulse inhibition disrupting effect of d-AMPH was found to be significantly reduced in the mutant mice. No significant differences between the cKO and control mice were observed in tests of anxiety, spatial learning and memory and social interaction. In- vivo microdialysis in the nucleus accumbens (NAc) showed a decrease in d-AMPH-induced extracellular DA release in the cKO mice. No significant alterations in protein levels of DA transporter, phosphorylated CaM kinase-II or Akt308 in the NAc were observed in the cKO mice. Taken together, our data suggest an important role of dysbindin-1 in maintaining mesolimbic DA tone and call for further investigations identifying mechanisms linking dysbindin-1, DA and schizophrenia.

Two mouse models carrying truncating mutations in Magel2 show distinct phenotypes

Schaaf-Yang syndrome (SYS) is a neurodevelopmental disorder caused by truncating variants in the paternal allele of MAGEL2, located in the Prader-Willi critical region, 15q11-q13. Although the phenotypes of SYS overlap those of Prader-Willi syndrome (PWS), including neonatal hypotonia, feeding problems, and developmental delay/intellectual disability, SYS patients show autism spectrum disorder and joint contractures, which are atypical phenotypes for PWS. Therefore, we hypothesized that the truncated Magel2 protein could potentially produce gain-of-function toxic effects. To test the hypothesis, we generated two engineered mouse models; one, an overexpression model that expressed the N-terminal region of Magel2 that was FLAG tagged with a strong ubiquitous promoter, and another, a genome-edited model that carried a truncating variant in Magel2 generated using the CRISPR/Cas9 system. In the overexpression model, all transgenic mice died in the fetal or neonatal period indicating embryonic or neonatal lethality of the transgene. Therefore, overexpression of the truncated Magel2 could show toxic effects. In the genome-edited model, we generated a mouse model carrying a frameshift variant (c.1690_1924del; p(Glu564Serfs*130)) in Magel2. Model mice carrying the frameshift variant in the paternal or maternal allele of Magel2 were termed Magel2^P:fs and Magel2^M:fs, respectively. The imprinted expression and spatial distribution of truncating Magel2 transcripts in the brain were maintained. Although neonatal Magel2^P:fs mice were lighter than wildtype littermates, Magel2^P:fs males and females weighed the same as their wildtype littermates by eight and four weeks of age, respectively. Collectively, the overexpression mouse model may recapitulate fetal or neonatal death, which are the severest phenotypes for SYS. In contrast, the genome-edited mouse model maintains genomic imprinting and distribution of truncated Magel2 transcripts in the brain, but only partially recapitulates SYS phenotypes. Therefore, our results imply that simple gain-of-function toxic effects may not explain the patho-mechanism of SYS, but rather suggest a range of effects due to Magel2 variants as in human SYS patients.

Are Circadian Disturbances a Core Pathophysiological Component of Schizophrenia?

Schizophrenia is a multifactorial disorder caused by a combination of genetic variations and exposure to environmental insults. Sleep and circadian rhythm disturbances are a prominent and ubiquitous feature of many psychiatric disorders, including schizophrenia. There is growing interest in uncovering the mechanistic link between schizophrenia and circadian rhythms, which may directly affect disorder outcomes. In this review, we explore the interaction between schizophrenia and circadian rhythms from 2 complementary angles. First, we review evidence that sleep and circadian rhythm disturbances constitute a fundamental component of schizophrenia, as supported by both human studies and animal models with genetic mutations related to schizophrenia. Second, we discuss the idea that circadian rhythm disruption interacts with existing risk factors for schizophrenia to promote schizophrenia-relevant behavioral and neurobiological abnormalities. Understanding the mechanistic link between schizophrenia and circadian rhythms will have implications for mitigating risk to the disorder and informing the development of circadian-based therapies.

Schizophrenia-associated gene dysbindin-1 and tardive dyskinesia

Tardive dyskinesia (TD) is a potentially irreversible movement disorder observed following long-term antipsychotic exposure. Its cause is unknown; however, a genetic component has been supported by studies of affected families. Dysbindin-1, encoded by the dystrobrevin-binding protein 1 DTNBP1 gene, has been associated with schizophrenia and is potentially involved in dopamine neurotransmission through its regulation of dopamine release and dopamine D2 receptor recycling, making it a candidate for investigation in TD. We investigated common variants across the DTNBP1 gene in our schizophrenia/patients with schizoaffective disorder of European ancestry. We found a number of DTNBP1 three-marker haplotypes to be associated with TD occurrence and TD severity (p < 0.05). These preliminary findings, if replicated in larger independent samples, would suggest that drugs targeting dysbindin-1 may be an option in the prevention and treatment of TD.

Retinal biomarkers and pharmacological targets for Hermansky-Pudlak syndrome 7

Deletion of dystrobrevin binding protein 1 has been linked to Hermansky-Pudlak syndrome type 7 (HPS-7), a rare disease characterized by oculocutaneous albinism and retinal dysfunction. We studied dysbindin-1 null mutant mice (Dys^−/−) to shed light on retinal neurodevelopment defects in HPS-7. We analyzed the expression of a focused set of miRNAs in retina of wild type (WT), Dys^+/− and Dys^−/− mice. We also investigated the retinal function of these mice through electroretinography (ERG). We found that miR-101-3p, miR-137, miR-186-5p, miR-326, miR-382-5p and miR-876-5p were up-regulated in Dys^−/−mice retina. Dys^−/− mice showed significant increased b-wave in ERG, compared to WT mice. Bioinformatic analysis highlighted that dysregulated miRNAs target synaptic plasticity and dopaminergic signaling pathways, affecting retinal functions of Dys^−/− mice. Overall, the data indicate potential mechanisms in retinal neurodevelopment of Dys^−/− mice, which may have translational significance in HSP-7 patients, both in terms of diagnostic/prognostic biomarkers and novel pharmacological targets.

Loss of dysbindin-1 affects GABAergic transmission in the PFC

It has been shown that dystrobrevin-binding protein 1 gene that encodes the protein dysbindin-1 is associated with risk for cognitive deficits, and studies have shown decreases in glutamate and correlated decreases in dysbindin-1 protein in the prefrontal cortex (PFC) and hippocampus of post-mortem tissue from schizophrenia patients. The PFC and the hippocampus have been shown to play a fundamental role in cognition, and studies in dysbindin-1 null mice have shown alterations in NMDAR located in pyramidal neurons as well as perturbation in LTP and cognitive deficits. The balance between excitatory and inhibitory transmission is crucial for normal cognitive functions; however, there is a dearth of information regarding the effects of loss of dysbindin-1 in GABAergic transmission. Using in vitro whole-cell clamp recordings, Western blots, and immunohistochemistry, we report here that dysbindin-1-deficient mice exhibit a significant decrease in the frequency of sIPSCs and in the amplitude of mIPSCs and significant decreases in PV staining and protein level. These results suggest that loss of dysbindin-1 affects GABAergic transmission at pre- and postsynaptic level and decreases parvalbumin markers.

Dysbindin-1 contributes to prefrontal cortical dendritic arbor pathology in schizophrenia

Deep layer III pyramidal cells in the dorsolateral prefrontal cortex (DLPFC) from subjects with schizophrenia and bipolar disorder previously were shown to exhibit dendritic arbor pathology. This study sought to determine whether MARCKS, its regulatory protein dysbindin-1, and two proteins, identified using microarray data, CDC42BPA and ARHGEF6, were associated with dendritic arbor pathology in the DLPFC from schizophrenia and bipolar disorder subjects. Using western blotting, relative protein expression was assessed in the DLPFC (BA 46) grey matter from subjects with schizophrenia (n = 19), bipolar disorder (n = 17) and unaffected control subjects (n = 19). Protein expression data were then correlated with dendritic parameter data obtained previously. MARCKS and dysbindin-1a expression levels did not differ among the three groups. Dysbindin-1b expression was 26% higher in schizophrenia subjects (p = 0.01) and correlated inversely with basilar dendrite length (r = -0.31, p = 0.048) and the number of spines per basilar dendrite (r = -0.31, p = 0.048), but not with dendritic spine density (r = -0.16, p = 0.32). The protein expression of CDC42BPA was 33% higher in schizophrenia subjects (p = 0.03) but, did not correlate with any dendritic parameter (p > 0.05). ARHGEF6 87 kDa isoform expression did not differ among the groups. CDC42BPA expression was not altered in frontal cortex from rats chronically administered haloperidol or clozapine. Dysbindin-1b appears to play a role in dendritic arbor pathology observed previously in the DLPFC in schizophrenia.

BLOC-1 is required for selective membrane protein trafficking from endosomes to primary cilia

Primary cilia perceive the extracellular environment through receptors localized in the ciliary membrane, but mechanisms directing specific proteins to this domain are poorly understood. To address this question, we knocked down proteins potentially important for ciliary membrane targeting and determined how this affects the ciliary trafficking of fibrocystin, polycystin-2, and smoothened. Our analysis showed that fibrocystin and polycystin-2 are dependent on IFT20, GMAP210, and the exocyst complex, while smoothened delivery is largely independent of these components. In addition, we found that polycystin-2, but not smoothened or fibrocystin, requires the biogenesis of lysosome-related organelles complex-1 (BLOC-1) for ciliary delivery. Consistent with the role of BLOC-1 in sorting from the endosome, we find that disrupting the recycling endosome reduces ciliary polycystin-2 and causes its accumulation in the recycling endosome. This is the first demonstration of a role for BLOC-1 in ciliary assembly and highlights the complexity of pathways taken to the cilium.

Evidence of an epistatic effect between Dysbindin-1 and Neuritin-1 genes on the risk for schizophrenia spectrum disorders

BACKGROUND

The interest in studying gene-gene interactions is increasing for psychiatric diseases such as schizophrenia-spectrum disorders (SSD), where multiple genes are involved. Dysbindin-1 (DTNBP1) and Neuritin-1 (NRN1) genes have been previously associated with SSD and both are involved in synaptic plasticity. We aimed to study whether these genes show an epistatic effect on the risk for SSD.

METHODS

The sample comprised 388 SSD patients and 397 healthy subjects. Interaction was tested between: (i) three DTNBP1 SNPs (rs2619537, rs2743864, rs1047631) related to changes in gene expression; and (ii) an haplotype in NRN1 previously associated with the risk for SSD (rs645649-rs582262: HAP-risk C-C).

RESULTS

An interaction between DTNBP1 rs2743864 and NRN1 HAP-risk was detected by using the model based multifactor dimensionality reduction (MB-MDR) approach (P=0.0049, after permutation procedure), meaning that the risk for SSD is significantly higher in those subjects carrying both the A allele of rs2743864 and the HAP-risk C-C. This interaction was confirmed by using a logistic regression model (P=0.033, OR (95%CI)=2.699 (1.08-6.71), R²=0.162).

DISCUSSION

Our results suggest that DTNBP1 and NRN1 genes show a joint effect on the risk for SSD. Although the precise mechanism underlying this effect is unclear, the fact that these genes have been involved in synaptic maturation, connectivity and glutamate signalling suggests that our findings could be of value as a link to the schizophrenia aetiology.

Schizophrenia susceptibility gene product dysbindin-1 regulates the homeostasis of cyclin D1

Dysbindin-1 (dystrobrevin binding protein-1, DTNBP1) is now widely accepted as a potential schizophrenia susceptibility gene and accumulating evidence indicates its functions in the neural development. In this study, we tried to identify new binding partners for dysbindin-1 to clarify the novel function of this molecule. When consulted with BioGRID protein interaction database, cyclin D3 was found to be a possible binding partner for dysbindin-1. We then examined the interaction between various dysbindin-1 isoforms (dysbindin-1A, -1B and -1C) and all three D-type cyclins (cyclin D1, D2, and D3) by immunoprecipitation with the COS7 cell expression system, and found that dysbindin-1A preferentially interacts with cyclin D1. The mode of interaction between these molecules was considered as direct binding since recombinant dysbindin-1A and cyclin D1 formed a complex in vitro. Mapping analyses revealed that the C-terminal region of dysbindin-1A binds to the C-terminal of cyclin D1. Consistent with the results of the biochemical analyses, endogenous dysbindin-1was partially colocalized with cyclin D1 in NIH3T3 fibroblast cells and in neuronal stem and/or progenitor cells in embryonic mouse brain. While co-expression of dysbindin-1A with cyclin D1 changed the localization of the latter from the nucleus to cytosol, cyclin D1-binding partner CDK4 inhibited the dysbindin-cyclin D1 interaction. Meanwhile, depletion of endogenous dysbindin-1A increased cyclin D1 expression. These results indicate that dysbindin-1A may control the cyclin D1 function spatiotemporally and might contribute to better understanding of the pathophysiology of dysbindin-1-associated disorders.

Striatal dopamine release in a schizophrenia mouse model measured by electrochemical amperometry in vivo

Schizophrenia is a severely devastating mental disorder, the pathological process of which is proposed to be associated with the dysfunction of dopaminergic transmission. Our previous results have demonstrated slower kinetics of transmitter release (glutamate release in hippocampus and norepinephrine release in adrenal slice) in a schizophrenia model, dysbindin null-sandy mice. However, whether dopaminergic transmission in the nigrostriatal pathway contributes to the pathology of dysbindin-/- mice remains unknown. Here, we have provided a step-by-step protocol to be applied in the in vivo amperometric recording of dopamine (DA) release from the mouse striatum evoked by an action potential (AP) pattern. With this protocol, AP pattern-dependent DA release was recorded from dysbindin-/- mice striatum in vivo. On combining amperometric recording in slices and electrophysiology, we found that in dysbindin-/- mice, (1) presynaptically, AP-pattern dependent dopamine overflow and uptake were intact in vivo; (2) the recycling of the dopamine vesicle pool remained unchanged. (3) Postsynaptically, the excitability of medium spiny neuron (MSN) was also normal, as revealed by patch-clamp recordings in striatal slices. Taken together, in contrast to reduced norepinephrine release in adrenal chromaffin cells, the dopaminergic transmission remains unchanged in the nigrostriatal pathway in dysbindin-/- mice, providing a new insight into the functions of the schizophrenia susceptibility gene dysbindin.

Increased dysbindin-1B isoform expression in schizophrenia and its propensity in aggresome formation

Genetic variations in the human dysbindin-1 gene (DTNBP1) have been associated with schizophrenia. As a result of alternative splicing, the human DTNBP1 gene generates at least three distinct protein isoforms, dysbindin-1A, -1B and -1C. Significant effort has focused on dysbindin-1A, an important player in multiple steps of neurodevelopment. However, the other isoforms, dysbindin-1B and dysbindin-1C have not been well characterized. Nor have been associated with human diseases. Here we report an increase in expression of DTNBP1b mRNA in patients with paranoid schizophrenia as compared with healthy controls. A single-nucleotide polymorphism located in intron 9, rs117610176, has been identified and associated with paranoid schizophrenia, and its C allele leads to an increase of DTNBP1b mRNA splicing. Our data show that different dysbindin splicing isoforms exhibit distinct subcellular distribution, suggesting their distinct functional activities. Dysbindin-1B forms aggresomes at the perinuclear region, whereas dysbindin-1A and -1C proteins exhibit diffused patterns in the cytoplasm. Dysbindin-1A interacts with dysbindin-1B, getting recruited to the aggresome structure when co-expressed with dysbindin-1B. Moreover, cortical neurons over-expressing dysbindin-1B show reduction in neurite outgrowth, suggesting that dysbindin-1B may interfere with dysbindin-1A function in a dominant-negative manner. Taken together, our study uncovers a previously unknown association of DTNBP1b expression with schizophrenia in addition to its distinct biochemical and functional properties.

The N-ethylmaleimide-sensitive factor and dysbindin interact to modulate synaptic plasticity

Dysbindin is a schizophrenia susceptibility factor and subunit of the biogenesis of lysosome-related organelles complex 1 (BLOC-1) required for lysosome-related organelle biogenesis, and in neurons, synaptic vesicle assembly, neurotransmission, and plasticity. Protein networks, or interactomes, downstream of dysbindin/BLOC-1 remain partially explored despite their potential to illuminate neurodevelopmental disorder mechanisms. Here, we conducted a proteome-wide search for polypeptides whose cellular content is sensitive to dysbindin/BLOC-1 loss of function. We identified components of the vesicle fusion machinery as factors downregulated in dysbindin/BLOC-1 deficiency in neuroectodermal cells and iPSC-derived human neurons, among them the N-ethylmaleimide-sensitive factor (NSF). Human dysbindin/BLOC-1 coprecipitates with NSF and vice versa, and both proteins colocalized in a Drosophila model synapse. To test the hypothesis that NSF and dysbindin/BLOC-1 participate in a pathway-regulating synaptic function, we examined the role for NSF in dysbindin/BLOC-1-dependent synaptic homeostatic plasticity in Drosophila. As previously described, we found that mutations in dysbindin precluded homeostatic synaptic plasticity elicited by acute blockage of postsynaptic receptors. This dysbindin mutant phenotype is fully rescued by presynaptic expression of either dysbindin or Drosophila NSF. However, neither reduction of NSF alone or in combination with dysbindin haploinsufficiency impaired homeostatic synaptic plasticity. Our results demonstrate that dysbindin/BLOC-1 expression defects result in altered cellular content of proteins of the vesicle fusion apparatus and therefore influence synaptic plasticity.

Genetic polymorphism in DTNBP1 gene is associated with methamphetamine-induced panic disorder

OBJECTIVE

The dysbindin-1 (dystrobrevin-binding protein-1 [DTNBP-1]) gene has repeatedly been shown to be associated with psychotic disorder across diverse populations. In this study, we attempted to investigate the association of the rs3213207 (P1635) genetic polymorphism of the DTNBP1 gene with methamphetamine dependence and with methamphetamine-induced psychosis, manic episodes, and panic disorder in a male Malaysian population.

METHODS

This polymorphism was genotyped in 233 male methamphetamine-dependent subjects and in 301 male controls of the following 4 different ethnicities: Malay, Chinese, Kadazan-Dusun, and Bajau. Intergroup statistical analyses were performed by using the χ(2) test and the Fisher exact test where necessary. In cases of multiple comparisons, the Bonferroni correction was performed.

RESULTS

Our results indicated that the DTNBP1 rs3213207 polymorphism did not show any significant association with risk of methamphetamine dependence, either in the pooled subjects or after stratification into the 4 different ethnic groups (P > 0.05). Furthermore, we did not find any association of this polymorphism with methamphetamine-induced psychosis and episodes of methamphetamine-induced mania. However, there was a strong association between this polymorphism and the occurrence of methamphetamine-induced panic disorder in the pooled subjects (odds ratio [OR] = 6.739, P < 0.001) and in the Malay (OR = 11.93, P = 0.022) and Kadazan-Dusun (OR = 115.0, P < 0.001) groups.

CONCLUSIONS

Our findings suggest that the DTNBP1 rs3213207 polymorphism may contribute to methamphetamine-induced panic disorder in the pooled Malaysian male population, especially in the Malay and Kadazan-Dusun ethnic groups. However, no association was found with methamphetamine dependence, methamphetamine-induced psychosis, or methamphetamine-induced mania.

Molecular basis of major psychiatric diseases such as schizophrenia and depression

Recently several potential susceptibility genes for major psychiatric disorders (schizophrenia and major depression) such as disrupted-in-schizophrenia 1(DISC1), dysbindin and pituitary adenylate cyclase-activating polypeptide (PACAP) have been reported. DISC1 is involved in neural development directly via adhesion molecules or via its binding partners of DISC1 such as elongation protein ζ-1 (FEZ1), DISC1-binding zinc-finger protein (DBZ) and kendrin. PACAP also regulates neural development via stathmin 1 or via regulation of the DISC1-DBZ binding. Dysbindin is also involved in neural development by regulating centrosomal microtubule network formation. All such molecules examined to date are involved in neural development. Thus, these findings provide new molecular insights into the mechanisms of neural development and neuropsychiatric disorders. On the other hand, in addition to neurons, both DISC and DBZ have been detected in oligodendrocytes and implicated in regulating oligodendrocyte differentiation. DISC1 inhibits the differentiation of oligodendrocyte precursor cells into oligodendrocytes, while DBZ has a positive regulatory role in oligodendrocyte differentiation. Evidence suggesting that disturbance of oligodendrocyte development causes major depression is also described.

Loss of dysbindin-1 in mice impairs reward-based operant learning by increasing impulsive and compulsive behavior

The dystrobrevin-binding protein 1 (DTNBP1) gene, which encodes the dysbindin-1 protein, is a potential schizophrenia susceptibility gene. Polymorphisms in the DTNBP1 gene have been associated with altered cognitive abilities. In the present study, dysbindin-1 null mutant (dys-/-), heterozygous (dys+/-), and wild-type (dys+/+) mice, on a C57BL/6J genetic background, were tested in either a match to sample or nonmatch to sample visual discrimination task. This visual discrimination task was designed to measure rule learning and detect any changes in response timing over the course of testing. Dys-/- mice displayed significant learning deficits and required more trials to acquire this task. However, once criterion was reached, there were no differences between the genotypes on any behavioral measures. Dys-/- mice exhibited increased compulsive and impulsive behaviors compared to control littermates suggesting the inability to suppress incorrectly-timed responses underlies their increased time to acquisition. Indeed, group comparisons of behavior differences between the first and last day of testing showed that only dys-/- mice consistently decreased measures of perseverative, premature, timeout, and total responses. These findings illustrate how some aspects of altered cognitive performance in dys-/- mice might be related to increased impulsive and compulsive behaviors, analogous to cognitive deficits in some individuals with psychiatric disorders.

Preliminary evidence for association between schizophrenia and polymorphisms in the regulatory Regions of the ADRA2A, DRD3 and SNAP-25 Genes

The results of linkage and candidate gene association studies have led to a range of hypotheses about the pathogenesis of schizophrenia. We limited our study to polymorphisms in candidate genes involved in dopaminergic and noradrenergic systems, and in the 25KDa synaptosomal-associated protein (SNAP-25) gene that is related to neurotransmitter exocytosis. Eight single nucleotide polymorphisms (SNPs) in regulating or coding regions of genes for the alpha-2A adrenergic receptor (ADRA2A), dopamine receptors D1 and D3 (DRD1 and DRD3), dopamine β-hydroxylase (DBH) and SNAP-25 were genotyped in male patients with schizophrenia (n=192) and in healthy controls (n=213). These polymorphisms were previously associated with schizophrenia. The allelic association between schizophrenia and ADRA2A rs1800544 polymorphism, SNAP-25 rs1503112 polymorphism, and DRD3 rs6280 polymorphism was found in our study. However, only observations for rs1503112 survived correction for multiple testing. Association was also evaluated by considering the polymorphisms as interactions; in this case, a likelihood ratio test (LRT) revealed evidence for association with schizophrenia in four polymorphism combinations: two DRD3*SNAP-25 combinations (rs6280*rs3746544 and rs6280*rs3746544, P=0.02), one ADRA2A*SNAP25 combination (rs1800544*rs3746544) and one ADRA2A*DBH combination (rs1800544*rs2519152). Our results are in agreement with the previously proposed role of DNA polymorphisms involved in dopaminergic, noradrenergic and synaptic functions in the pathogenesis of schizophrenia. Further relevant studies including larger sample size and more markers are needed to confirm our results.

Dysbindin-1 modulates prefrontal cortical activity and schizophrenia-like behaviors via dopamine/D2 pathways

Dysbindin-1 regulates D2-receptor trafficking and is implicated in schizophrenia and related cognitive abnormalities, but whether this molecular effect mediates the clinical manifestations of the disorder is unknown. We explored in dysbindin-1-deficient mice (dys-/-) (1) schizophrenia-related behaviors, (2) molecular and electrophysiological changes in medial prefrontal cortex (mPFC) and (3) the dependence of these on D2-receptor stimulation. Dysbindin-1 disruption altered dopamine-related behaviors and impaired working memory under challenging/stressful conditions. Dys-/- pyramidal neurons in mPFC layers II/III were hyperexcitable at baseline but hypoexcitable following D2 stimulation. Dys-/- were also respectively more and less sensitive to D2 agonist- and antagonist-induced behavioral effects. Dys-/- had reduced expression of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and CaMKKβ in mPFC. Chronic D2 agonist treatment reproduced these changes in protein expression, and some of the dys-/- behavioral effects. These results elucidate dysbindin's modulation of D2-related behavior, cortical activity and mPFC CaMK components, implicating cellular and molecular mechanisms of the association of dysbindin with psychosis.

Dystrobrevin-binding protein 1 gene (DTNBP1) variants associated with cerebrospinal fluid homovanillic acid and 5-hydroxyindoleacetic acid concentrations in healthy volunteers

The dystrobrevin binding protein-1 (DTNBP1) gene encodes dysbindin-1, a protein involved in neurodevelopmental and neurochemical processes related mainly to the monoamine dopamine. We investigated possible associations between eleven DTNBP1 polymorphisms and cerebrospinal fluid (CSF) concentrations of the major dopamine metabolite homovanillic acid (HVA), the major serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), and the major noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy human subjects (n=132). Two polymorphisms, rs2619538 and rs760666, were nominally associated with CSF HVA and 5-HIAA concentrations, whereas a third polymorphism, rs909706, showed association only with HVA. After correction for multiple testing only the associations between rs2619538 and HVA and 5-HIAA concentrations remained significant. No significant association was found between any of the investigated DTNBP1 polymorphisms and CSF MHPG concentrations. The results suggest that genetic variation in DTNBP1 gene affects the regulation of dopamine and serotonin turnover in the central nervous system of healthy volunteers.

Dysbindin-containing complexes and their proposed functions in brain: from zero to (too) many in a decade

Dysbindin (also known as dysbindin-1 or dystrobrevin-binding protein 1) was identified 10 years ago as a ubiquitously expressed protein of unknown function. In the following years, the protein and its encoding gene, DTNBP1, have become the focus of intensive research owing to genetic and histopathological evidence suggesting a potential role in the pathogenesis of schizophrenia. In this review, we discuss published results demonstrating that dysbindin function is required for normal physiology of the mammalian central nervous system. In tissues other than brain and in non-neuronal cell types, the protein has been characterized as a stable component of a multi-subunit complex, named BLOC-1 (biogenesis of lysosome-related organelles complex-1), which has been implicated in intracellular protein trafficking and the biogenesis of specialized organelles of the endosomal-lysosomal system. In the brain, however, dysbindin has been proposed to associate into multiple complexes with alternative binding partners, and to play a surprisingly wide variety of functions including transcriptional regulation, neurite and dendritic spine formation, synaptic vesicle biogenesis and exocytosis, and trafficking of glutamate and dopamine receptors. This puzzling array of molecular and functional properties ascribed to the dysbindin protein from brain underscores the need of further research aimed at ascertaining its biological significance in health and disease.

Dysbindin-1 gene contributes differentially to early- and adult-onset forms of functional psychosis

Dysbindin-1 is a relatively ubiquitous protein in the brain which is involved in the modulation of synaptic homeostasis. The dysbindin-1 gene (DTNBP1) has been associated with schizophrenia and bipolar disorder diagnoses. However, its contribution to the severity of the clinical and neurocognitive expression of these disorders remains controversial. We aimed to explore the association between DTNBP1 and the phenotypes which are more directly linked with the underlying biology, such as age at onset and neurocognitive impairment. The present family sample comprised 894 Caucasian individuals: 268 patients affected by functional psychosis [58% with illness onset before 18 years, mean age at onset (SD): 14.71 (2.10)], 483 parents and 143 siblings. Ten DTNBP1 single nucleotide polymorphisms were genotyped in all individuals and their transmission disequilibrium was tested in relation to: (i) the risk for psychosis; (ii) patients' age at onset; and (iii) familial neurocognitive performance (including IQ estimation and executive functioning). In early-onset families a 5-marker haplotype encompassing exons 2-4 and the surrounding introns was significantly over-transmitted to cases, while in adult-onset families two haplotypes corresponding to the region between introns 4 and 7 were over-transmitted to cases. Estimated IQ was associated with the rs760666 marker in the whole sample, whereas a significant association between executive functioning and the rs2619522 marker appeared in early-onset families. Our findings confirm the role of the dysbindin-1 gene in the risk for functional psychosis and show a differential haplotypic risk pattern in families with early as opposed to adult onset in the affected offspring.

Dysbindin-1 genotype effects on emotional working memory

We combined functional imaging and genetics to investigate the behavioral and neural effects of a dysbindin-1 (DTNBP1) genotype associated with the expression level of this important synaptic protein, which has been implicated in schizophrenia. On a working memory (WM) task for emotional faces, participants with the genotype related to increased expression showed higher WM capacity for happy faces compared with the genotype related to lower expression. Activity in several task-related brain areas with known DTNBP1 expression was increased, including hippocampal, temporal and frontal cortex. Although these increases occurred across emotions, they were mostly observed in areas whose activity correlated with performance for happy faces. This suggests effects of variability in DTNBP1 on emotion-specific WM capacity and region-specific task-related brain activation in humans. Synaptic effects of DTNBP1 implicate that altered dopaminergic and/or glutamatergic neurotransmission may be related to the increased WM capacity. The combination of imaging and genetics thus allows us to bridge the gap between the cellular/molecular and systems/behavioral level and extend the cognitive neuroscience approach to a comprehensive biology of cognition.

Reduced rate of neural differentiation in the dentate gyrus of adult dysbindin null (sandy) mouse

Genetic variations in the gene encoding dysbindin has consistently been associated with schizophrenia and bipolar disorder, although little is known about the neural functions carried out by dysbindin. To gain some insight into this area, we took advantage of the readily available dysbindin-null mouse sandy (sdy−/−) and studied hippocampal neurogenesis using thymidine analogue bromodeoxuridine (BrdU). No significant differences were found in the proliferation (4 hours) or survival (1, 4 and 8 weeks after the last BrdU injection) of progenitors in the subgranular regions of the dentate gyrus between sdy−/− and sdy+/+ (control) mice. However, 4 weeks after the last BrdU injection, a significant reduction was observed in the ratio of neuronal differentiation in sdy−/− when compared to that of sdy+/+ (sdy+/+  = 87.0±5.3% vs. sdy−/−  = 71.3±8.3%, p = 0.01). These findings suggest that dysbindin plays a role during differentiation process in the adult hippocampal neurogenesis and that its deficit may negatively affect neurogenesis-related functions such as cognition and mood.

Nucleocytoplasmic shuttling of dysbindin-1, a schizophrenia-related protein, regulates synapsin I expression

Dysbindin-1 is a 50-kDa coiled-coil-containing protein encoded by the gene DTNBP1 (dystrobrevin-binding protein 1), a candidate genetic factor for schizophrenia. Genetic variations in this gene confer a susceptibility to schizophrenia through a decreased expression of dysbindin-1. It was reported that dysbindin-1 regulates the expression of presynaptic proteins and the release of neurotransmitters. However, the precise functions of dysbindin-1 are largely unknown. Here, we show that dysbindin-1 is a novel nucleocytoplasmic shuttling protein and translocated to the nucleus upon treatment with leptomycin B, an inhibitor of exportin-1/CRM1-mediated nuclear export. Dysbindin-1 harbors a functional nuclear export signal necessary for its nuclear export, and the nucleocytoplasmic shuttling of dysbindin-1 affects its regulation of synapsin I expression. In brains of sandy mice, a dysbindin-1-null strain that displays abnormal behaviors related to schizophrenia, the protein and mRNA levels of synapsin I are decreased. These findings demonstrate that the nucleocytoplasmic shuttling of dysbindin-1 regulates synapsin I expression and thus may be involved in the pathogenesis of schizophrenia.

Dysbindin-1, WAVE2 and Abi-1 form a complex that regulates dendritic spine formation

Genetic variations in dysbindin-1 (dystrobrevin-binding protein-1) are one of the most commonly reported variations associated with schizophrenia. As schizophrenia could be regarded as a neurodevelopmental disorder resulting from abnormalities of synaptic connectivity, we attempted to clarify the function of dysbindin-1 in neuronal development. We examined the developmental change of dysbindin-1 in rat brain by western blotting and found that a 50 kDa isoform is highly expressed during the embryonic stage, whereas a 40 kDa one is detected at postnatal day 11 and increased thereafter. Immunofluorescent analyses revealed that dysbindin-1 is enriched at the spine-like structure of primary cultured rat hippocampal neurons. We identified WAVE2, but not N-WASP, as a binding partner for dysbindin-1. We also found that Abi-1, a binding molecule for WAVE2 involved in spine morphogenesis, interacts with dysbindin-1. Although dysbindin-1, WAVE2 and Abi-1 form a ternary complex, dysbindin-1 promoted the binding of WAVE2 to Abi-1. RNA interference-mediated knockdown of dysbindin-1 led to the generation of abnormally elongated immature dendritic protrusions. The present results indicate possible functions of dysbindin-1 at the postsynapse in the regulation of dendritic spine morphogenesis through the interaction with WAVE2 and Abi-1.

A polymorphism in the dysbindin gene (DTNBP1) associated with multiple psychiatric disorders including schizophrenia

BACKGROUND

A number of studies have found associations between dysbindin (DTNBP1) polymorphisms and schizophrenia. Recently we identified a DTNBP1 SNP (rs9370822) that is strongly associated with schizophrenia. Individuals diagnosed with schizophrenia were nearly three times as likely to carry the CC genotype compared to the AA genotype.

METHODS

To investigate the importance of this SNP in the function of DTNBP1, a number of psychiatric conditions including addictive behaviours and anxiety disorders were analysed for association with rs9370822.

RESULTS

The DTNBP1 polymorphism was significantly associated with post-traumatic stress disorder (PTSD) as well as nicotine and opiate dependence but not alcohol dependence. Individuals suffering PTSD were more than three times as likely to carry the CC genotype compared to the AA genotype. Individuals with nicotine or opiate dependence were more than twice as likely to carry the CC genotype compared to the AA genotype.

CONCLUSIONS

This study provides further support for the importance of DTNBP1 in psychiatric conditions and suggests that there is a common underlying molecular defect involving DTNBP1 that contributes to the development of several anxiety and addictive disorders that are generally recognised as separate clinical conditions. These disorders may actually be different expressions of a single metabolic pathway perturbation. As our participant numbers are limited our observations should be viewed with caution until they are independently replicated.

Mouse behavioral endophenotypes for schizophrenia

An endophenotype is a heritable trait that is generally considered to be more highly, associated with a gene-based neurological deficit than a disease phenotype itself. Such, endophenotypic deficits may therefore be observed in the non-affected relatives of disease patients. Once endophenotypes have been established for a given illness, such as schizophrenia, mechanisms of, action may then be established and treatment options developed in order to target such measures. The, current paper describes and assesses the merits and limitations of utilizing behavioral and, electrophysiological endophenotypes of schizophrenia in mice. Such endophenotypic deficits include: decreased auditory event related potential (ERP) amplitude and gating (specifically, that of the P20, N40, P80 and P120); impaired mismatch negativity (MMN); changes in theta and gamma frequency, analyses; decreased pre-pulse inhibition (PPI); impaired working and episodic memories (for instance, novel object recognition [NOR], contextual and cued fear conditioning, latent inhibition, Morris and, radial arm maze identification and nose poke); sociability; and locomotor activity. A variety of, pharmacological treatments, including ketamine, MK-801 and phencyclidine (PCP) can be used to, induce some of the deficits described above, and numerous transgenic mouse strains have been, developed to address the mechanisms responsible for such endophenotypic differences. We also, address the viability and validity of using such measures regarding their potential clinical implications, and suggest several practices that could increase the translatability of preclinical data.

Dysbindin promotes the post-endocytic sorting of G protein-coupled receptors to lysosomes

Background

Dysbindin, a cytoplasmic protein long known to function in the biogenesis of specialized lysosome-related organelles (LROs), has been reported to reduce surface expression of D2 dopamine receptors in neurons. Dysbindin is broadly expressed, and dopamine receptors are members of the large family of G protein-coupled receptors (GPCRs) that function in diverse cell types. Thus we asked if dysbindin regulates receptor number in non-neural cells, and further investigated the cellular basis of this regulation.

Methodology/Principal Findings

We used RNA interference to deplete endogenous dysbindin in HEK293 and HeLa cells, then used immunochemical and biochemical methods to assess expression and endocytic trafficking of epitope-tagged GPCRs. Dysbindin knockdown up-regulated surface expression of D2 receptors compared to D1 receptors, as reported previously in neurons. This regulation was not mediated by a change in D2 receptor endocytosis. Instead, dysbindin knockdown specifically reduced the subsequent trafficking of internalized D2 receptors to lysosomes. This distinct post-endocytic sorting function explained the minimal effect of dysbindin depletion on D1 receptors, which recycle efficiently and traverse the lysosomal pathway to only a small degree. Moreover, dysbindin regulated the delta opioid receptor, a more distantly related GPCR that is also sorted to lysosomes after endocytosis. Dysbindin was not required for lysosomal trafficking of all signaling receptors, however, as its depletion did not detectably affect down-regulation of the EGF receptor tyrosine kinase. Dysbindin co-immunoprecipitated with GASP-1 (or GPRASP-1), a cytoplasmic protein shown previously to modulate lysosomal trafficking of D2 dopamine and delta opioid receptors by direct interaction, and with HRS that is a core component of the conserved ESCRT machinery mediating lysosome biogenesis and sorting.

Conclusions/Significance

These results identify a distinct, and potentially widespread function of dysbindin in promoting the sorting of specific GPCRs to lysosomes after endocytosis.

The dysbindin-containing complex (BLOC-1) in brain: developmental regulation, interaction with SNARE proteins and role in neurite outgrowth

Previous studies have implicated DTNBP1 as a schizophrenia susceptibility gene and its encoded protein, dysbindin, as a potential regulator of synaptic vesicle physiology. In this study, we found that endogenous levels of the dysbindin protein in the mouse brain are developmentally regulated, with higher levels observed during embryonic and early postnatal ages than in young adulthood. We obtained biochemical evidence indicating that the bulk of dysbindin from brain exists as a stable component of biogenesis of lysosome-related organelles complex-1 (BLOC-1), a multi-subunit protein complex involved in intracellular membrane trafficking and organelle biogenesis. Selective biochemical interaction between brain BLOC-1 and a few members of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) superfamily of proteins that control membrane fusion, including SNAP-25 and syntaxin 13, was demonstrated. Furthermore, primary hippocampal neurons deficient in BLOC-1 displayed neurite outgrowth defects. Taken together, these observations suggest a novel role for the dysbindin-containing complex, BLOC-1, in neurodevelopment, and provide a framework for considering potential effects of allelic variants in DTNBP1--or in other genes encoding BLOC-1 subunits--in the context of the developmental model of schizophrenia pathogenesis.

Dysbindin regulates the transcriptional level of myristoylated alanine-rich protein kinase C substrate via the interaction with NF-YB in mice brain

Background

An accumulating body of evidence suggests that Dtnbp1 (Dysbindin) is a key susceptibility gene for schizophrenia. Using the yeast-two-hybrid screening system, we examined the candidate proteins interacting with Dysbindin and revealed one of these candidates to be the transcription factor NF-YB.

Methods

We employed an immunoprecipitation (IP) assay to demonstrate the Dysbindin-NF-YB interaction. DNA chips were used to screen for altered expression of genes in cells in which Dysbindin or NF-YB was down regulated, while Chromatin IP and Reporter assays were used to confirm the involvement of these genes in transcription of Myristoylated alanine-rich protein kinase C substrate (MARCKS). The sdy mutant mice with a deletion in Dysbindin, which exhibit behavioral abnormalities, and wild-type DBA2J mice were used to investigate MARCKS expression.

Results

We revealed an interaction between Dysbindin and NF-YB. DNA chips showed that MARCKS expression was increased in both Dysbindin knockdown cells and NF-YB knockdown cells, and Chromatin IP revealed interaction of these proteins at the MARCKS promoter region. Reporter assay results suggested functional involvement of the interaction between Dysbindin and NF-YB in MARCKS transcription levels, via the CCAAT motif which is a NF-YB binding sequence. MARCKS expression was increased in sdy mutant mice when compared to wild-type mice.

Conclusions

These findings suggest that abnormal expression of MARCKS via dysfunction of Dysbindin might cause impairment of neural transmission and abnormal synaptogenesis. Our results should provide new insights into the mechanisms of neuronal development and the pathogenesis of schizophrenia.

Dysfunction of dopamine release in the prefrontal cortex of dysbindin deficient sandy mice: an in vivo microdialysis study

Dystrobrevin binding protein-1 gene (DTNBP1), which encodes dysbindin protein, has been identified as a schizophrenia susceptibility gene. Dysbindin has been shown to contribute to the regulation of exocytosis and formation of synaptic vesicles. Although hypofrontality in schizophrenia underlies its pathophysiology, the molecular function of dysbindin in synaptic neurotransmission remains unclear. In the present study, we investigated depolarization-evoked dopamine (DA) and serotonin (5-HT) release in the prefrontal cortex (PFC) of sandy (sdy) mice, which have a deletion mutation in the gene encoding DTNBP1. In vivo microdialysis analysis revealed that extracellular DA levels in the PFC of wild-type mice were increased by 60mM KCl stimulation, and the KCl-evoked DA release was significantly decreased in sdy mice compared with wild-type mice. Extracellular 5-HT levels in the PFC of wild-type mice were also increased by 60mM KCl stimulation. The KCl-evoked 5-HT release did not differ between wild-type and sdy mice. There was no difference in basal levels of DA and 5-HT before the stimulation between two groups. Behavioral sensitization after repeated methamphetamine (METH) treatment was significantly reduced in sdy mice compared with wild-type mice whereas no difference was observed in METH-induced hyperlocomotion between two groups. These results suggest that dysbindin may have a role in the regulation of depolarization-evoked DA release in the PFC and in the development of behavioral sensitization induced by repeated METH treatment.

Role of dysbindin in dopamine receptor trafficking and cortical GABA function

Dysbindin has been implicated in the pathogenesis of schizophrenia, but little is known about how dysbindin affects neuronal function in the circuitry underlying psychosis and related behaviors. Using a dysbindin knockout line (dys(-/-)) derived from the natural dysbindin mutant Sandy mice, we have explored the role of dysbindin in dopamine signaling and neuronal function in the prefrontal cortex (PFC). Combined cell imaging and biochemical experiments revealed a robust increase in the dopamine receptor D2, but not D1, on cell surface of neurons from dys(-/-) cortex. This was due to an enhanced recycling and insertion, rather than reduced endocytosis, of D2. Disruption of dysbindin gene resulted in a marked decrease in the excitability of fast-spiking (FS) GABAergic interneurons in both PFC and striatum. Dys(-/-) mice also exhibited a decreased inhibitory input to pyramidal neurons in layer V of PFC. The increased D2 signaling in dys(-/-) FS interneurons was associated with a more pronounced increase in neuronal firing in response to D2 agonist, compared to that in wild-type interneurons. Taken together, these results suggest that dysbindin regulates PFC function by facilitating D2-mediated modulation of GABAergic function.

Evidence that putative ADHD low risk alleles at SNAP25 may increase the risk of schizophrenia

Synaptosomal Associated Protein 25 kDa (SNAP25) has been implicated in the pathogenesis of schizophrenia by numerous neuropathological studies and genetic variation at SNAP25 has been reported to be associated with ADHD. Expression levels of the putative schizophrenia susceptibility gene DTNBP1 has been shown to influence the levels of SNAP25 in vitro. We undertook directed mutation screening of SNAP25 in UK schizophrenic cases followed by direct association analysis of all variants identified and identified known exonic SNPs that showed evidence for association (rs3746544 P = 0.004 OR = 1.26, rs8636 P = 0.003 OR = 1.27), although these SNPs are highly correlated (r(2) > 0.99). We additionally genotyped a further 31 tag SNPs spanning the SNAP25 locus and identified several independent SNPs that were nominally associated with schizophrenia (strongest association at rs3787283, P = 0.006, OR = 1.25) however, due to the number of tests performed no SNP met experiment-wise significance (minimum permuted P-value = 0.1). Post hoc analysis revealed that the SNPs nominally associated with schizophrenia (rs3787283, rs3746544) were the same as those previously demonstrated to be associated with ADHD but with the opposite alleles, allowing the intriguing hypothesis that genetic variation at SNAP25 may be differentially associated with both schizophrenia and ADHD.

Association between the dysbindin gene (DTNBP1) and cognitive functions in Japanese subjects

AIM

The dysbindin gene (dystrobrevin binding protein 1: DTNBP1) is a susceptibility gene for schizophrenia. Susceptibility genes for schizophrenia have been hypothesized to mediate liability for the disorder at least partly by influencing cognitive performance. This report investigated the relationship between cognitive function and the dysbindin gene.

METHODS

The possible association between a single nucleotide polymorphism (SNP) of DTNBP1 (rs2619539: P1655), which is a risk-independent SNP for schizophrenia in Japanese populations, and memory and IQ was investigated in 70 schizophrenia patients and 165 healthy volunteers in a Japanese population.

RESULTS

This SNP was associated with two memory scales, verbal memory and general memory, on the Wechsler Memory Scale-Revised (WMS-R), and three subcategories of the Wechsler Adult Intelligence Scale-Revised (WAIS-R), vocabulary, similarities and picture completion in healthy subjects. The SNP, however, did not influence either the indices of WMS-R, IQ or subcategories of WAIS-R in schizophrenia patients.

CONCLUSION

A risk-independent SNP in DTNBP1 may have an impact on cognitive functions such as memory and IQ in healthy subjects.

Proteomic analysis reveals novel binding partners of dysbindin, a schizophrenia-related protein

Schizophrenia is a complex mental disorder with fairly high level of heritability. Dystrobrevin binding protein 1, a gene encoding dysbindin protein, is a susceptibility gene for schizophrenia that was identified by family-based association analysis. Recent studies revealed that dysbindin is involved in the exocytosis and/or formation of synaptic vesicles. However, the molecular function of dysbindin in synaptic transmission is largely unknown. To investigate the signaling pathway in which dysbindin is involved, we isolated dysbindin-interacting molecules from rat brain lysate by combining ammonium sulfate precipitation and dysbindin-affinity column chromatography, and identified dysbindin-interacting proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and liquid chromatography-tandem mass spectrometry. Proteins involved in protein localization process, including Munc18-1, were identified as dysbindin-interacting proteins. Munc18-1 was co-immunoprecipitated with dysbindin from rat brain lysate, and directly interacted with dysbindin in vitro. In primary cultured rat hippocampal neurons, a part of dysbindin was co-localized with Munc18-1 at pre-synaptic terminals. Our result suggests a role for dysbindin in synaptic vesicle exocytosis via interaction with Munc18-1.

Association analysis between schizophrenia and the AP-3 complex genes

A susceptibility gene for schizophrenia, dysbindin, is a component of BLOC-1, which interacts with the adaptor protein (AP)-3 complex. As a direct interaction between dysbindin and AP-3 complex was reported, we examined a possible association between 16 SNPs in the AP3 complex genes and schizophrenia using 432 cases and 656 controls. Nominal association between rs6688 in the AP3M1 gene and schizophrenia (chi(2)=6.33, P=0.012, odds ratio=0.80) was no longer positive after correction for multiple testing (corrected P=0.192). The present results suggest that AP3 complex genes might not play a major role in the pathogenesis of schizophrenia in this population.

The BLOC interactomes form a network in endosomal transport

With the identification of more than a dozen novel Hermansky-Pudlak Syndrome (HPS) proteins in vesicle trafficking in higher eukaryotes, a new class of trafficking pathways has been described. It mainly consists of three newly-defined protein complexes, BLOC-1, -2, and -3. Compelling evidence indicates that these complexes together with two other well-known complexes, AP3 and HOPS, play important roles in endosomal transport. The interactions between these complexes form a network in protein trafficking via endosomes and cytoskeleton. Each node of this network has intra-complex and extra-complex interactions. These complexes are connected by direct interactions between the subunits from different complexes or by indirect interactions through coupling nodes that interact with two or more subunits from different complexes. The dissection of this network facilitates the understanding of a dynamic but elaborate transport machinery in protein/membrane trafficking. The disruption of this network may lead to abnormal trafficking or defective organellar development as described in patients with Hermansky-Pudlak syndrome.

Direct interaction of Dysbindin with the AP-3 complex via its mu subunit

Genetic factors are important in the etiology of schizophrenia. Recent studies have revealed the association between genetic variation of Dysbindin (DTNBP1) and schizophrenia. Dysbindin is one of the essential components of the biogenesis of lysosome-related organelles complex 1 (BLOC-1). BLOC-1 physically interacts with the adaptor protein (AP)-3 complex, which is essential for vesicle or protein sorting. However, it remains largely unknown how BLOC-1 interacts with the AP-3 complex. To investigate the binding mode of BLOC-1 and the AP-3 complex, we examined the relation between Dysbindin and the AP-3 complex and found that Dysbindin formed a complex with the AP-3 complex through the direct binding to its mu subunit. Dysbindin partially co-localized with the AP-3 complex in CA1 and CA3 of mouse hippocampus, and at presynaptic terminals and axonal growth cones of cultured hippocampal neurons. Suppression of Dysbindin results in the reduction of presynaptic protein expression and glutamate release. Thus, Dysbindin appears to participate in the exocytosis or sorting of the synaptic vesicle via direct interaction with the AP-3 complex.

Dysbindin-1, a schizophrenia-related protein, functionally interacts with the DNA- dependent protein kinase complex in an isoform-dependent manner

DTNBP1 has been recognized as a schizophrenia susceptible gene, and its protein product, dysbindin-1, is down-regulated in the brains of schizophrenic patients. However, little is known about the physiological role of dysbindin-1 in the central nervous system. We hypothesized that disruption of dysbindin-1 with unidentified proteins could contribute to pathogenesis and the symptoms of schizophrenia. GST pull-down from human neuroblastoma lysates showed an association of dysbindin-1 with the DNA-dependent protein kinase (DNA-PK) complex. The DNA-PK complex interacts only with splice isoforms A and B, but not with C. We found that isoforms A and B localized in nucleus, where the kinase complex exist, whereas the isoform C was found exclusively in cytosol. Furthermore, results of phosphorylation assay suggest that the DNA-PK complex phosphorylated dysbindin-1 isoforms A and B in cells. These observations suggest that DNA-PK regulates the dysbindin-1 isoforms A and B by phosphorylation in nucleus. Isoform C does not contain exons from 1 to 6. Since schizophrenia-related single nucleotide polymorphisms (SNPs) occur in these introns between exon 1 and exon 6, we suggest that these SNPs might affect splicing of DTNBP1, which leads to impairment of the functional interaction between dysbindin-1 and DNA-PK in schizophrenic patients.

New findings from genetic association studies of schizophrenia

In the past 20 years, association studies of schizophrenia have evolved from analyses in lesser than 100 subjects of one or two markers in candidate genes to systematic analyses of association at a genome-wide level in samples of thousands of subjects. During this process, much of the emergent literature has been difficult to interpret and definitive findings that have met with universal acceptance have been elusive, largely because studies have been underpowered for such conclusions to be drawn. Nevertheless, in the course of the past few years, a few promising candidate genes have been reported for which the evidence is positive across multiple studies, and more recently, genome-wide association studies have yielded findings of a compelling nature. It is clear that genetic studies in schizophrenia have borne fruit, a process that can be expected to accelerate in the next few years, and that these findings are providing new avenues for research into the pathophysiology of this poorly understood disorder.

Impaired long-term memory retention and working memory in sdy mutant mice with a deletion in Dtnbp1, a susceptibility gene for schizophrenia

BACKGROUND

Schizophrenia is a complex genetic disorder caused by multiple genetic and environmental factors. The dystrobrevin-binding protein 1 (DTNBP1: dysbindin-1) gene is a major susceptibility gene for schizophrenia. Genetic variations in DTNBP1 are associated with cognitive functions, general cognitive ability and memory function, and clinical features of patients with schizophrenia including negative symptoms and cognitive decline. Since reduced expression of dysbindin-1 has been observed in postmortem brains of patients with schizophrenia, the sandy (sdy) mouse, which has a deletion in the Dtnbp1 gene and expresses no dysbindin-1 protein, could be an animal model of schizophrenia. To address this issue, we have carried out a comprehensive behavioral analysis of the sdy mouse in this study.

RESULTS

In a rotarod test, sdy mice did not exhibit motor learning whilst the wild type mice did. In a Barnes circular maze test both sdy mice and wild type mice learned to selectively locate the escape hole during the course of the training period and in the probe trial conducted 24 hours after last training. However, sdy mice did not locate the correct hole in the retention probe tests 7 days after the last training trial, whereas wild type mice did, indicating impaired long-term memory retention. A T-maze forced alternation task, a task of working memory, revealed no effect of training in sdy mice despite the obvious effect of training in wild type mice, suggesting a working memory deficit.

CONCLUSION

Sdy mouse showed impaired long-term memory retention and working memory. Since genetic variation in DTNBP1 is associated with both schizophrenia and memory function, and memory function is compromised in patients with schizophrenia, the sdy mouse may represent a useful animal model to investigate the mechanisms of memory dysfunction in the disorder.

Behavioral characterization of dysbindin-1 deficient sandy mice

Dysbindin-1 (dystrobrevin binding protein-1) has been reported as a candidate gene associated with schizophrenia. Dysbindin-1 mRNA and protein levels are significantly reduced in the prefrontal cortex and hippocampus of schizophrenia subjects. To understand the in-vivo functions of dysbindin-1, we studied schizophrenia relevant behaviors in adult male Sandy homozygous (sdy/sdy) and heterozygous (sdy/+) mice that have a natural mutation in dysbindin-1 gene (on a DBA/2J background) resulting in loss of protein expression. Spontaneous locomotor activity of sdy/sdy and sdy/+ mice in novel environment was not significantly different from DBA/2J controls. However, on repeated testing in the same environment for 7 days, sdy/sdy mice, in contrast to DBA/2J controls showed a lack of locomotor habituation. Locomotor activating effect of a low dose of d-amphetamine (2.5 mg/kg i.p.), a behavioral measure of mesolimbic dopamine activity, was significantly reduced in the mutant mice. Interestingly, sdy/sdy mice showed enhanced locomotor sensitization to repeated five daily injection of amphetamine. Possible cognitive impairment in Sandy mutants was revealed in novel object recognition test as sdy/sdy and sdy/+ mice spent significantly less time exploring novel objects compared to DBA/2J. Sdy/sdy mice also showed deficits in emotionally motivated learning and memory showing greater freezing response to auditory conditioned stimulus (CS) in fear conditioning paradigm. In thermal nociceptive test, the latency of paw withdrawal in sdy/sdy and sdy/+ animals was significantly higher compared to DBA/2J indicating hypoalgesia in the mutants. Taken together, these data suggest that dysbindin-1 gene deficiency leads to significant changes in cognition and altered responses to psychostimulants.