Neurobehavioral abnormalities in the dysbindin-1 mutant, sandy, on a C57BL/6J genetic background

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.

Large structural variants in KOLF2.1J are unlikely to compromise neurological disease modelling

Gracia-Diaz and colleagues analysed high-density DNA microarray and whole genome sequencing (WGS) data from the KOLF2.1J 'reference' human induced pluripotent stem cell (hiPSC) line1, and report the presence of five high-confidence heterozygous copy number variants (CNVs) at least 100kbp in length2. Since three of these CNVs span coding genes, some of which have been associated with neurodevelopmental disease, the authors raise the concern that these CNVs may compromise the utility of KOLF2.1J for neurological disease modelling. We appreciate their thorough analysis and thoughtful interpretation, and agree that potential users of this line should be made aware of all cases where KOLF2.1J differs from the reference genome. However, we believe that the benefits from the widespread use of KOLF2.1J outweigh the potential risks that might arise from the identified CNVs.

The translational genetics of ADHD and related phenotypes in model organisms

Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent neurodevelopmental disorder resulting from the interaction between genetic and environmental risk factors. It is well known that ADHD co-occurs frequently with other psychiatric disorders due, in part, to shared genetics factors. Although many studies have contributed to delineate the genetic landscape of psychiatric disorders, their specific molecular underpinnings are still not fully understood. The use of animal models can help us to understand the role of specific genes and environmental stimuli-induced epigenetic modifications in the pathogenesis of ADHD and its comorbidities. The aim of this review is to provide an overview on the functional work performed in rodents, zebrafish and fruit fly and highlight the generated insights into the biology of ADHD, with a special focus on genetics and epigenetics. We also describe the behavioral tests that are available to study ADHD-relevant phenotypes and comorbid traits in these models. Furthermore, we have searched for new models to study ADHD and its comorbidities, which can be useful to test potential pharmacological treatments.

Exposure to Circadian Disruption During Adolescence Interacts With a Genetic Risk Factor to Modify Schizophrenia-relevant Behaviors in a Sex-dependent Manner

DTNBP1 is a gene associated with schizophrenia. Postmortem studies found a reduced expression of DTNBP1 in regions associated with schizophrenia in patients' brains. Sandy (Sdy) mice have a loss-of-function mutation in Dtnbp1 gene, resulting in behavioral deficits and brain changes similar to those seen in patients with schizophrenia. We previously showed that exposing adult Sdy mice to circadian disruption led to an exacerbation of schizophrenia-relevant behaviors. Here we asked whether the interaction between this genetic risk factor and circadian disruption occurs during adolescence, a period when environmental insults can promote schizophrenia symptoms, and whether sex affects this interaction. Starting at postnatal day 21, wild-type (WT) and Sdy males and females were housed for 4 weeks either in a 12 h light:12 h dark (LD 12:12) cycle or under chronic jetlag (CJL). Then, after 2 weeks in LD 12:12, behavioral assessments were conducted, including elevated plus maze (EPM), novel object recognition (NOR), social interaction, and prepulse inhibition (PPI) of acoustic startle. NOR and social novelty tests showed that, surprisingly, CJL during adolescence had opposite effects on WT and Sdy males, that is, behavioral deficits in WT males while rescuing preexisting deficits in Sdy mice. CJL led to decreased sociability in WT and Sdy mice while decreasing PPI only in females. Sdy mice showed decreased anxiety-like behavior compared with wild-type (WT), which was further accentuated by CJL in males. Thus, circadian disruption during adolescence, on its own or in association with Dtnbp1 mutation, can influence cognition, sociability, sensorimotor gating, and anxiety-like behaviors in a sex-dependent manner.

Genetics, molecular control and clinical relevance of habituation learning

Habituation is the most fundamental form of learning. As a firewall that protects our brain from sensory overload, it is indispensable for cognitive processes. Studies in humans and animal models provide increasing evidence that habituation is affected in autism and related monogenic neurodevelopmental disorders (NDDs). An integrated application of habituation assessment in NDDs and their animal models has unexploited potential for neuroscience and medical care. With the aim to gain mechanistic insights, we systematically retrieved genes that have been demonstrated in the literature to underlie habituation. We identified 258 evolutionarily conserved genes across species, describe the biological processes they converge on, and highlight regulatory pathways and drugs that may alleviate habituation deficits. We also summarize current habituation paradigms and extract the most decisive arguments that support the crucial role of habituation for cognition in health and disease. We conclude that habituation is a conserved, quantitative, cognition- and disease-relevant process that can connect preclinical and clinical work, and hence is a powerful tool to advance research, diagnostics, and treatment of NDDs.

Advantages and Limitations of Animal Schizophrenia Models

Mental illness modeling is still a major challenge for scientists. Animal models of schizophrenia are essential to gain a better understanding of the disease etiopathology and mechanism of action of currently used antipsychotic drugs and help in the search for new and more effective therapies. We can distinguish among pharmacological, genetic, and neurodevelopmental models offering various neuroanatomical disorders and a different spectrum of symptoms of schizophrenia. Modeling schizophrenia is based on inducing damage or changes in the activity of relevant regions in the rodent brain (mainly the prefrontal cortex and hippocampus). Such artificially induced dysfunctions approximately correspond to the lesions found in patients with schizophrenia. However, notably, animal models of mental illness have numerous limitations and never fully reflect the disease state observed in humans.

Dysbindin-1, BDNF, and GABAergic Transmission in Schizophrenia

Schizophrenia is a psychiatric disorder characterized by hallucinations, anhedonia, disordered thinking, and cognitive impairments. Both genetic and environmental factors contribute to schizophrenia. Dysbindin-1 (DTNBP1) and brain-derived neurotrophic factor (BDNF) are both genetic factors associated with schizophrenia. Mice lacking Dtnbp1 showed behavioral deficits similar to human patients suffering from schizophrenia. DTNBP1 plays important functions in synapse formation and maintenance, receptor trafficking, and neurotransmitter release. DTNBP1 is co-assembled with 7 other proteins into a large protein complex, known as the biogenesis of lysosome-related organelles complex-1 (BLOC-1). Large dense-core vesicles (LDCVs) are involved in the secretion of hormones and neuropeptides, including BDNF. BDNF plays important roles in neuronal development, survival, and synaptic plasticity. BDNF is also critical in maintaining GABAergic inhibitory transmission in the brain. Two studies independently showed that DTNBP1 mediated activity-dependent BDNF secretion to maintain inhibitory transmission. Imbalance of excitatory and inhibitory neural activities is thought to contribute to schizophrenia. In this mini-review, we will discuss a potential pathogenetic mechanism for schizophrenia involving DTNBP1, BDNF, and inhibitory transmission. We will also discuss how these processes are interrelated and associated with a higher risk of schizophrenia development.

Cortical copper transporter expression in schizophrenia: interactions of risk gene dysbindin-1

Schizophrenia susceptibility factor dysbindin-1 is associated with cognitive processes. Downregulated dysbindin-1 expression is associated with lower expression of copper transporters ATP7A and CTR1, required for copper transport to the central nervous system. We measured dysbindin-1 isoforms-1A and -1BC, CTR1, and ATP7A via Western blots of the postmortem dorsolateral prefrontal cortex (DLPFC) of schizophrenia subjects (n = 28) and matched controls (n = 14). In addition, we subdivided the schizophrenia group by treatment status and comorbidity of alcohol use disorder (AUD) and assessed the relationships between proteins. Schizophrenia subjects exhibited similar protein levels to that of controls, with no effect of antipsychotic treatment. We observed a shift towards more dysbindin-1A expression in schizophrenia, as revealed by the ratio of dysbindin-1 isoforms. Dysbindin-1A expression was negatively correlated with ATP7A in schizophrenia, with no correlation present in controls. AUD subjects exhibited less dysbindin-1BC and CTR1 than those without AUD. Our results, taken together with previous data, suggest that alterations in dysbindin-1 and copper transporters are brain-region specific. For example, protein levels of ATP7A, dysbindin 1BC, and CTR1 are lower in the substantia nigra in schizophrenia subjects. AUD in the DLPFC was associated with lower protein levels of dysbindin-1 and CTR1. Changes in dysbindin-1 isoform ratio and relationships appear to be prevalent in the disease, potentially impacting symptomology.

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.

Current landscape of Oculocutaneous Albinism in Japan

Oculocutaneous albinism (OCA), which is roughly divided into non-syndromic and syndromic OCA, is a group of autosomal recessive disorders caused by mutations in genes associated with pigmentation. Patients with OCA have hypopigmentation and ocular manifestations such as photophobia, amblyopia, and nystagmus. Hermansky-Pudlak syndrome (HPS), the most common syndromic OCA, is characterized by the additional features of a bleeding tendency and other critical systemic comorbidities such as pulmonary fibrosis and immunodeficiency. NGS-based gene analyses have identified several new causative genes for OCA and have detected rare subtypes of OCA with high accuracy including Japanese patients. In our survey of 190 Japanese OCA patients/families, OCA4 is the most common subtype (25.3%) followed by OCA1 (20.0%), HPS1 (14.7%), and OCA2 (8.4%). Similar to the A481T variant in OCA2, which is associated with a mild form of OCA2 and skin color variation, the c.-492_489delAATG variant located in the promoter region of SLC45A2 has been uniquely identified in Japanese patients with a mild form of OCA4. Further, rare OCA subtypes, including OCA3, HPS2, HPS3, HPS4, HPS5, HPS6, and HPS9, have also been identified in Japanese patients. The clinical characteristics and underlying molecular mechanisms of each subtype of OCA are concisely summarized in this review.

Ethologically based behavioural and neurochemical characterisation of mice with isoform-specific loss of dysbindin-1A in the context of schizophrenia

Dysbindin-1 is implicated in several aspects of schizophrenia, including cognition and both glutamatergic and dopaminergic neurotransmission. Targeted knockout of dysbindin-1A (Dys-1A KO), the most abundant and widely expressed isoform in the brain, is associated with deficits in delay/interference-dependent working memory. Using an ethologically based approach, the following behavioural phenotypes were examined in Dys-1A KO mice: exploratory activity, social interaction, anxiety and problem-solving ability. Levels of monoamines and their metabolites were measured in striatum, hippocampus and prefrontal cortex using high-performance liquid chromatography with electrochemical detection. The ethogram of initial exploration in Dys-1A KO mice was characterised by increased rearing from a seated position; over subsequent habituation, stillness was decreased relative to wildtype. In a test of dyadic social interaction with an unfamiliar conspecific in a novel environment, female KO mice showed an increase in investigative social behaviours. Marble burying behaviour was unchanged. Using the puzzle-box test to measure general problem-solving performance, no effect of genotype was observed across nine trials of increasing complexity. Dys-1A KO demonstrated lower levels of 5-HT in ratio to its metabolite 5-HIAA in the prefrontal cortex. These studies elaborate the behavioural and neurochemical phenotype of Dys-1A KO mice, revealing subtle genotype-related differences in non-social and social exploratory behaviours and habituation of exploration in a novel environment, as well as changes in 5-HT activity in brain areas related to schizophrenia.

Interactions between knockout of schizophrenia risk factor Dysbindin-1 and copper metabolism in mice

BACKGROUND AND PURPOSE

DTNBP1 gene variation and lower dysbindin-1 protein are associated with schizophrenia. Previous evidence suggests that downregulated dysbindin-1 expression results in lower expression of copper transporters ATP7A (intracellular copper transporter) and SLC31A1 (CTR1; extracellular copper transporter), which are required for copper transport across the blood brain barrier. However, whether antipsychotic medications used for schizophrenia treatment may modulate these systems is unclear.

EXPERIMENTAL APPROACH

The current study measured behavioral indices of neurological function in dysbindin-1 functional knockout (KO) mice and their wild-type (WT) littermates with or without quetiapine treatment. We assessed serum and brain copper levels, ATP7A and CTR1 mRNA, and copper transporter-expressing cellular population transcripts: TTR (transthyretin; choroid plexus epithelial cells), MBP (myelin basic protein; oligodendrocytes), and GJA1 (gap-junction protein alpha-1; astrocytes) in cortex and hippocampus.

KEY RESULTS

Regardless of genotype, quetiapine significantly reduced TTR, MBP, CTR1 mRNA, and serum copper levels. Neurological function of untreated KO mice was abnormal, and ledge instability was rescued with quetiapine. KO mice were hyperactive after 10 min in the open-field assay, which was not affected by treatment.

CONCLUSIONS AND IMPLICATIONS

Dysbindin-1 KO results in hyperactivity, altered serum copper, and neurological impairment, the last of which is selectively rescued with quetiapine. Antipsychotic treatment modulates specific cellular populations, affecting myelin, the choroid plexus, and copper transport across the blood brain barrier. Together these results indicate the widespread impact of antipsychotic treatment, and that alteration of dysbindin-1 may be sufficient, but not necessary, for specific schizophrenia pathology.

Histone deacetylase-3: Friend and foe of the brain

IMPACT STATEMENT

Brain development and degeneration are highly complex processes that are regulated by a large number of molecules and signaling pathways the identities of which are being unraveled. Accumulating evidence points to histone deacetylases and epigenetic mechanisms as being important regulators of these processes. In this review, we describe that histone deacetylase-3 (HDAC3) is a particularly crucial regulator of both neurodevelopment and neurodegeneration. In addition, HDAC3 regulates memory formation, synaptic plasticity, and the cognitive impairment associated with normal aging. Understanding how HDAC3 functions contributes to the normal development and functioning of the brain while also promoting neurodegeneration could lead to the development of therapeutic approaches for neurodevelopmental, neuropsychiatric, and neurodegenerative disorders.

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.

Sex-dimorphic effects of biogenesis of lysosome-related organelles complex-1 deficiency on mouse perinatal brain development

The function(s) of the Biogenesis of Lysosome-related Organelles Complex-1 (BLOC-1) during brain development is to date largely unknown. Here, we investigated how its absence alters the trajectory of postnatal brain development using as model the pallid mouse. Most of the defects observed early postnatally in the mutant mice were more prominent in males than in females and in the hippocampus. Male mutant mice, but not females, had smaller brains as compared to sex-matching wild types at postnatal day 1 (P1), this deficit was largely recovered by P14 and P45. An abnormal cytoarchitecture of the pyramidal cell layer of the hippocampus was observed in P1 pallid male, but not female, or juvenile mice (P45), along with severely decreased expression levels of the radial glial marker Glutamate-Aspartate Transporter. Transcriptomic analyses showed that the overall response to the lack of functional BLOC-1 was more pronounced in hippocampi at P1 than at P45 or in the cerebral cortex. These observations suggest that absence of BLOC-1 renders males more susceptible to perinatal brain maldevelopment and although most abnormalities appear to have been resolved in juvenile animals, still permanent defects may be present, resulting in faulty neuronal circuits, and contribute to previously reported cognitive and behavioral phenotypes in adult BLOC-1-deficient mice.

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.

Developmental Genes and Regulatory Proteins, Domains of Cognitive Impairment in Schizophrenia Spectrum Psychosis and Implications for Antipsychotic Drug Discovery: The Example of Dysbindin-1 Isoforms and Beyond

Alongside positive and negative symptomatology, deficits in working memory, attention, selective learning processes, and executive function have been widely documented in schizophrenia spectrum psychosis. These cognitive abnormalities are strongly associated with impairment across multiple function domains and are generally treatment-resistant. The DTNBP1 (dystrobrevin-binding protein-1) gene, encoding dysbindin, is considered a risk factor for schizophrenia and is associated with variation in cognitive function in both clinical and nonclinical samples. Downregulation of DTNBP1 expression in dorsolateral prefrontal cortex and hippocampal formation of patients with schizophrenia has been suggested to serve as a primary pathophysiological process. Described as a "hub," dysbindin is an important regulatory protein that is linked with multiple complexes in the brain and is involved in a wide variety of functions implicated in neurodevelopment and neuroplasticity. The expression pattern of the various dysbindin isoforms (-1A, -1B, -1C) changes depending upon stage of brain development, tissue areas and subcellular localizations, and can involve interaction with different protein partners. We review evidence describing how sequence variation in DTNBP1 isoforms has been differentially associated with schizophrenia-associated symptoms. We discuss results linking these isoform proteins, and their interacting molecular partners, with cognitive dysfunction in schizophrenia, including evidence from drosophila through to genetic mouse models of dysbindin function. Finally, we discuss preclinical evidence investigating the antipsychotic potential of molecules that influence dysbindin expression and functionality. These studies, and other recent work that has extended this approach to other developmental regulators, may facilitate identification of novel molecular pathways leading to improved antipsychotic treatments.

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.

Deletion of Dtnbp1 in mice impairs threat memory consolidation and is associated with enhanced inhibitory drive in the amygdala

Schizophrenia is a severe and highly heritable disorder. Dystrobrevin-binding protein 1 (DTNBP1), also known as dysbindin-1, has been implicated in the pathophysiology of schizophrenia. Specifically, dysbindin-1 mRNA and protein expression are decreased in the brains of subjects with this disorder. Mice lacking dysbinidn-1 also display behavioral phenotypes similar to those observed in schizophrenic patients. However, it remains unknown whether deletion of dysbindin-1 impacts functions of the amygdala, a brain region that is critical for emotional processing, which is disrupted in patients with schizophrenia. Here, we show that dysbindin-1 is expressed in both excitatory and inhibitory neurons of the basolateral amygdala (BLA). Deletion of dysbindin-1 in male mice (Dys-/-) impaired cued and context-dependent threat memory, without changes in measures of anxiety. The behavioral deficits observed in Dys-/- mice were associated with perturbations in the BLA, including the enhancement of GABAergic inhibition of pyramidal neurons, increased numbers of parvalbumin interneurons, and morphological abnormalities of dendritic spines on pyramidal neurons. Our findings highlight an important role for dysbindin-1 in the regulation of amygdalar function and indicate that enhanced inhibition of BLA pyramidal neuron activity may contribute to the weakened threat memory expression observed in Dys-/- mice.

An Overview of Animal Models Related to Schizophrenia

Schizophrenia is a heterogeneous psychiatric disorder that is poorly treated with current therapies. In this brief review, we provide an update regarding the use of animal models to study schizophrenia in an attempt to understand its aetiology and develop novel therapeutic strategies. Tremendous progress has been made developing and validating rodent models that replicate the aetiologies, brain pathologies, and behavioural abnormalities associated with schizophrenia in humans. Here, models are grouped into 3 categories-developmental, drug induced, and genetic-to reflect the heterogeneous risk factors associated with schizophrenia. Each of these models is associated with varied but overlapping pathophysiology, endophenotypes, behavioural abnormalities, and cognitive impairments. Studying schizophrenia using multiple models will permit an understanding of the core features of the disease, thereby facilitating preclinical research aimed at the development and validation of better pharmacotherapies to alter the progression of schizophrenia or alleviate its debilitating symptoms.

Sleep/Wake Disruption in a Mouse Model of BLOC-1 Deficiency

Mice lacking a functional Biogenesis of Lysosome-related Organelles Complex 1 (BLOC-1), such as those of the pallid line, display cognitive and behavioural impairments reminiscent of those presented by individuals with intellectual and developmental disabilities. Although disturbances in the sleep/wake cycle are commonly lamented by these individuals, the underlying mechanisms, including the possible role of the circadian timing system, are still unknown. In this paper, we have explored sleep/circadian malfunctions and underlying mechanisms in BLOC-1-deficient pallid mice. These mutants exhibited less sleep behaviour in the beginning of the resting phase than wild-type mice with a more broken sleeping pattern in normal light-dark conditions. Furthermore, the strength of the activity rhythms in the mutants were reduced with significantly more fragmentation and lower precision than in age-matched controls. These symptoms were accompanied by an abnormal preference for the open arm in the elevated plus maze in the day and poor performance in the novel object recognition at night. At the level of the central circadian clock (the suprachiasmatic nucleus, SCN), loss of BLOC-1 caused subtle morphological changes including a larger SCN and increased expression of the relative levels of the clock gene Per2 product during the day but did not affect the neuronal activity rhythms. In the hippocampus, the pallid mice presented with anomalies in the cytoarchitecture of the Dentate Gyrus granule cells, but not in CA1 pyramidal neurones, along with altered PER2 protein levels as well as reduced pCREB/tCREB ratio during the day. Our findings suggest that lack of BLOC-1 in mice disrupts the sleep/wake cycle and performance in behavioural tests associated with specific alterations in cytoarchitecture and protein expression.

Pallidin is a novel interacting protein for cytohesin-2 and regulates the early endosomal pathway and dendritic formation in neurons

Cytohesin-2 is a member of the guanine nucleotide exchange factors for ADP ribosylation factor 1 (Arf1) and Arf6, which are small GTPases that regulate membrane traffic and actin dynamics. In this study, we first demonstrated that cytohesin-2 localized to the plasma membrane and vesicles in various subcellular compartment in hippocampal neurons by immunoelectron microscopy. Next, to understand the molecular network of cytohesin-2 in neurons, we conducted yeast two-hybrid screening of brain cDNA libraries using cytohesin-2 as bait and isolated pallidin, a component of the biogenesis of lysosome-related organelles complex 1 (BLOC-1) involved in endosomal trafficking. Pallidin interacted specifically with cytohesin-2 among cytohesin family members. Glutathione S-transferase pull-down and immunoprecipitation assays further confirmed the formation of a protein complex between cytohesin-2 and pallidin. Immunofluorescence demonstrated that cytohesin-2 and pallidin partially colocalized in various subsets of endosomes immunopositive for EEA1, syntaxin 12, and LAMP2 in hippocampal neurons. Knockdown of pallidin or cytohesin-2 reduced cytoplasmic EEA1-positive early endosomes. Furthermore, knockdown of pallidin increased the total dendritic length of cultured hippocampal neurons, which was rescued by co-expression of wild-type pallidin but not a mutant lacking the ability to interact with cytohesin-2. In contrast, knockdown of cytohesin-2 had the opposite effect on total dendritic length. The present results suggested that the interaction between pallidin and cytohesin-2 may participate in various neuronal functions such as endosomal trafficking and dendritic formation in hippocampal neurons. Cover Image for this issue: doi: 10.1111/jnc.14197.

Impaired copper transport in schizophrenia results in a copper-deficient brain state: A new side to the dysbindin story

Objectives: Several schizophrenia brain regions exhibit decreased dysbindin. Dysbindin modulates copper transport crucial for myelination, monoamine metabolism and cellular homeostasis. Schizophrenia patients (SZP) exhibit increased plasma copper, while copper-decreasing agents produce schizophrenia-like behavioural and pathological abnormalities. Therefore, we sought to determine dysbindin and copper transporter protein expression and copper content in SZP.Methods: We studied the copper-rich substantia nigra (SN) using Western blot and inductively-coupled plasma mass spectrometry. We characterised specific protein domains of copper transporters ATP7A, CTR1, ATP7B and dysbindin isoforms 1 A and 1B/C in SZP (n = 15) and matched controls (n = 11), and SN copper content in SZP (n = 14) and matched controls (n = 11). As a preliminary investigation, we compared medicated (ON; n = 11) versus unmedicated SZP (OFF; n = 4).Results: SZP exhibited increased C terminus, but not N terminus, ATP7A. SZP expressed less transmembrane CTR1 and dysbindin 1B/C than controls. ON exhibited increased C terminus ATP7A protein versus controls. OFF exhibited less N terminus ATP7A protein than controls and ON, suggesting medication-induced rescue of the ATP7A N terminus. SZP exhibited less SN copper content than controls.Conclusions: These results provide the first evidence of disrupted copper transport in schizophrenia SN that appears to result in a copper-deficient state. Furthermore, copper homeostasis may be modulated by specific dysbindin isoforms and antipsychotic treatment.

A meta-analytic approach to genes that are associated with impaired and elevated spatial memory performance

Spatial memory deficits are a common hallmark of psychiatric conditions, possibly due to a genetic predisposition. Thus, unravelling the relationship between genes and memory might suggest novel therapeutic targets and pathogenetic pathways. Genetic deletions are known to lead to memory deficits (post-deletion "forgetfulness" genes, PDF), or, in few instances to improve spatial memory (post-deletion "hypermnesic" genes, PDH). To assess this topic, we performed a meta-analytic approach on memory behavior in knock-out mice. We screened 300 studies from PubMed and retrieved 87 genes tested for possible effects on spatial memory. This database was crossed with the Allen Brain Atlas (brain distribution) and the Enrichr (gene function) databases. The results show that PDF genes have higher expression level in several ventral brain structures, particularly the encephalic trunk and in the hypothalamus. Moreover, part of these genes are implicated in synaptic functions. Conversely, the PDH genes are associated to G-protein coupled receptors downstream signalling. Some candidate drugs were also found to interfere with some of the PDH genes, further suggesting that this approach might help in identifying drugs to improve memory performance in psychiatric conditions.

Single point mutation on the gene encoding dysbindin results in recognition deficits

The dystrobrevin-binding protein 1 (DTNBP1) gene is a candidate risk factor for schizophrenia and has been associated with cognitive ability in both patient populations and healthy controls. DTNBP1 encodes dysbindin protein, which is localized to synaptic sites and is reduced in the prefrontal cortex and hippocampus of patients with schizophrenia, indicating a potential role in schizophrenia etiology. Most studies of dysbindin function have focused on the sandy (sdy) mice that lack dysbindin protein and have a wide range of abnormalities. In this study, we examined dysbindin salt and pepper (spp) mice that possess a single point mutation on the Dtnbp1 gene predicted to reduce, but not eliminate, dysbindin expression. By western blot analysis, we found that spp homozygous (spp -/-) mutants had reduced dysbindin and synaptosomal-associated protein 25 (SNAP-25) in the prefrontal cortex, but unaltered levels in hippocampus. Behaviorally, spp mutants performed comparably to controls on a wide range of tasks assessing locomotion, anxiety, spatial recognition and working memory. However, spp -/- mice had selective deficits in tasks measuring novel object recognition and social novelty recognition. Our results indicate that reduced dysbindin and SNAP-25 protein in the prefrontal cortex of spp -/- is associated with selective impairments in recognition processing. These spp mice may prove useful as a novel mouse model to study cognitive deficits linked to dysbindin alterations. Our findings also suggest that aspects of recognition memory may be specifically influenced by DTNBP1 single nucleotide polymorphisms or risk haplotypes in humans and this connection should be further investigated.

Neurodevelopmental disease mechanisms, primary cilia, and endosomes converge on the BLOC-1 and BORC complexes

The biogenesis of lysosome-related organelles complex-1 (BLOC-1) and the bloc-one-related complex (BORC) are the cytosolic protein complexes required for specialized membrane protein traffic along the endocytic route and the spatial distribution of endosome-derived compartments, respectively. BLOC-1 and BORC complex subunits and components of their interactomes have been associated with the risk and/or pathomechanisms of neurodevelopmental disorders. Thus, cellular processes requiring BLOC-1 and BORC interactomes have the potential to offer novel insight into mechanisms underlying behavioral defects. We focus on interactions between BLOC-1 or BORC subunits with the actin and microtubule cytoskeleton, membrane tethers, and SNAREs. These interactions highlight requirements for BLOC-1 and BORC in membrane movement by motors, control of actin polymerization, and targeting of membrane proteins to specialized cellular domains such as the nerve terminal and the primary cilium. We propose that the endosome-primary cilia pathway is an underappreciated hub in the genesis and mechanisms of neurodevelopmental disorders. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 311-330, 2018.

Dysbindin-1 Involvement in the Etiology of Schizophrenia

Schizophrenia is a major psychiatric disorder that afflicts about 1% of the world’s population, falling into the top 10 medical disorders causing disability. Existing therapeutic strategies have had limited success on cognitive impairment and long-term disability and are burdened by side effects. Although new antipsychotic medications have been launched in the past decades, there has been a general lack of significant innovation. This lack of significant progress in the pharmacotherapy of schizophrenia is a reflection of the complexity and heterogeneity of the disease. To date, many susceptibility genes have been identified to be associated with schizophrenia. DTNBP1 gene, which encodes dysbindin-1, has been linked to schizophrenia in multiple populations. Studies on genetic variations show that DTNBP1 modulate prefrontal brain functions and psychiatric phenotypes. Dysbindin-1 is enriched in the dorsolateral prefrontal cortex and hippocampus, while postmortem brain studies of individuals with schizophrenia show decreased levels of dysbindin-1 mRNA and protein in these brain regions. These studies proposed a strong connection between dysbindin-1 function and the pathogenesis of disease. Dysbindin-1 protein was localized at both pre- and post-synaptic sites, where it regulates neurotransmitter release and receptors signaling. Moreover, dysbindin-1 has also been found to be involved in neuronal development. Reduced expression levels of dysbindin-1 mRNA and protein appear to be common in dysfunctional brain areas of schizophrenic patients. The present review addresses our current knowledge of dysbindin-1 with emphasis on its potential role in the schizophrenia pathology. We propose that dysbindin-1 and its signaling pathways may constitute potential therapeutic targets in the therapy of schizophrenia.

The Proteome of BLOC-1 Genetic Defects Identifies the Arp2/3 Actin Polymerization Complex to Function Downstream of the Schizophrenia Susceptibility Factor Dysbindin at the Synapse

Proteome modifications downstream of monogenic or polygenic disorders have the potential to uncover novel molecular mechanisms participating in pathogenesis and/or extragenic modification of phenotypic expression. We tested this idea by determining the proteome sensitive to genetic defects in a locus encoding dysbindin, a protein required for synapse biology and implicated in schizophrenia risk. We applied quantitative mass spectrometry to identify proteins expressed in neuronal cells the abundance of which was altered after downregulation of the schizophrenia susceptibility factor dysbindin (Bloc1s8) or two other dysbindin-interacting polypeptides, which assemble into the octameric biogenesis of lysosome-related organelles complex 1 (BLOC-1). We found 491 proteins sensitive to dysbindin and BLOC-1 loss of function. Gene ontology of these 491 proteins singled out the actin cytoskeleton and the actin polymerization factor, the Arp2/3 complex, as top statistical molecular pathways contained within the BLOC-1-sensitive proteome. Subunits of the Arp2/3 complex were downregulated by BLOC-1 loss of function, thus affecting actin dynamics in early endosomes of BLOC-1-deficient cells. Furthermore, we demonstrated that Arp2/3, dysbindin, and subunits of the BLOC-1 complex biochemically and genetically interact, modulating Drosophila melanogaster synapse morphology and homeostatic synaptic plasticity. Our results indicate that ontologically prioritized proteomics identifies novel pathways that modify synaptic phenotypes associated with neurodevelopmental disorder gene defects.

SIGNIFICANCE STATEMENT

The mechanisms associated with schizophrenia are mostly unknown despite the increasing number of genetic loci identified that increase disease risk. We present an experimental strategy that impartially and comprehensively interrogates the proteome of neurons to identify effects of genetic mutations in a schizophrenia risk factor, dysbindin. We find that the expression of the actin polymerization complex Arp2/3 is reduced in dysbindin-deficient cells, thus affecting actin-dependent phenotypes in two cellular compartments where dysbindin resides, endosomes and presynapses. Our studies indicate that a central cellular structure affected by schizophrenia susceptibility loci is the actin cytoskeleton, an organelle necessary for synaptic function in the presynaptic and postsynaptic compartment.

Dysregulation of Specialized Delay/Interference-Dependent Working Memory Following Loss of Dysbindin-1A in Schizophrenia-Related Phenotypes

Dysbindin-1, a protein that regulates aspects of early and late brain development, has been implicated in the pathobiology of schizophrenia. As the functional roles of the three major isoforms of dysbindin-1, (A, B, and C) remain unknown, we generated a novel mutant mouse, dys-1A-/-, with selective loss of dysbindin-1A and investigated schizophrenia-related phenotypes in both males and females. Loss of dysbindin-1A resulted in heightened initial exploration and disruption in subsequent habituation to a novel environment, together with heightened anxiety-related behavior in a stressful environment. Loss of dysbindin-1A was not associated with disruption of either long-term (olfactory) memory or spontaneous alternation behavior. However, dys-1A-/- showed enhancement in delay-dependent working memory under high levels of interference relative to controls, ie, impairment in sensitivity to the disruptive effect of such interference. These findings in dys-1A-/- provide the first evidence for differential functional roles for dysbindin-1A vs dysbindin-1C isoforms among phenotypes relevant to the pathobiology of schizophrenia. Future studies should investigate putative sex differences in these phenotypic effects.

Gene × Environment Interactions in Schizophrenia: Evidence from Genetic Mouse Models

The study of gene × environment, as well as epistatic interactions in schizophrenia, has provided important insight into the complex etiopathologic basis of schizophrenia. It has also increased our understanding of the role of susceptibility genes in the disorder and is an important consideration as we seek to translate genetic advances into novel antipsychotic treatment targets. This review summarises data arising from research involving the modelling of gene × environment interactions in schizophrenia using preclinical genetic models. Evidence for synergistic effects on the expression of schizophrenia-relevant endophenotypes will be discussed. It is proposed that valid and multifactorial preclinical models are important tools for identifying critical areas, as well as underlying mechanisms, of convergence of genetic and environmental risk factors, and their interaction in schizophrenia.

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.

Effects of sex and DTNBP1 (dysbindin) null gene mutation on the developmental GluN2B-GluN2A switch in the mouse cortex and hippocampus

BACKGROUND

Neurodevelopmental disorders such as autism spectrum disorders and schizophrenia differentially impact males and females and are highly heritable. The ways in which sex and genetic vulnerability influence the pathogenesis of these disorders are not clearly understood. The n-methyl-d-aspartate (NMDA) receptor pathway has been implicated in schizophrenia and autism spectrum disorders and changes dramatically across postnatal development at the level of the GluN2B-GluN2A subunit "switch" (a shift from reliance on GluN2B-containing receptors to reliance on GluN2A-containing receptors). We investigated whether sex and genetic vulnerability (specifically, null mutation of DTNBP1 [dysbindin; a possible susceptibility gene for schizophrenia]) influence the developmental GluN2B-GluN2A switch.

METHODS

Subcellular fractionation to enrich for postsynaptic density (PSD), together with Western blotting and kinase assay, were used to investigate the GluN2B-GluN2A switch in the cortex and hippocampus of male and female DTNBP1 null mutant mice and their wild-type littermates. Main effects of sex and DTNBP1 genotype, and interactions with age, were assessed using factorial ANOVA.

RESULTS

Sex differences in the GluN2B-GluN2A switch emerged across development at the frontal cortical synapse, in parameters related to GluN2B. Males across genotypes displayed higher GluN2B:GluN2A and GluN2B:GluN1 ratios (p < 0.05 and p < 0.01, respectively), higher GluN2B phosphorylation at Y1472 (p < 0.01), and greater abundance of PLCγ (p < 0.01) and Fyn (p = 0.055) relative to females. In contrast, effects of DTNBP1 were evident exclusively in the hippocampus. The developmental trajectory of GluN2B was disrupted in DTNBP1 null mice (genotype × age interaction p < 0.05), which also displayed an increased synaptic GluN2A:GluN1 ratio (p < 0.05) and decreased PLCγ (p < 0.05) and Fyn (only in females; p < 0.0005) compared to wild-types.

CONCLUSIONS

Sex and DTNBP1 mutation influence the GluN2B-GluN2A switch at the synapse in a brain-region-specific fashion involving pY1472-GluN2B, Fyn, and PLCγ. This highlights the possible mechanisms through which risk factors may mediate their effects on vulnerability to disorders of NMDA receptor dysfunction.

Molecular genetic models related to schizophrenia and psychotic illness: heuristics and challenges

Schizophrenia is a heritable disorder that may involve several common genes of small effect and/or rare copy number variation, with phenotypic heterogeneity across patients. Furthermore, any boundaries vis-à-vis other psychotic disorders are far from clear. Consequently, identification of informative animal models for this disorder, which typically relate to pharmacological and putative pathophysiological processes of uncertain validity, faces considerable challenges. In juxtaposition, the majority of mutant models for schizophrenia relate to the functional roles of a diverse set of genes associated with risk for the disorder or with such putative pathophysiological processes. This chapter seeks to outline the evidence from phenotypic studies in mutant models related to schizophrenia. These have commonly assessed the degree to which mutation of a schizophrenia-related gene is associated with the expression of several aspects of the schizophrenia phenotype or more circumscribed, schizophrenia-related endophenotypes; typically, they place specific emphasis on positive and negative symptoms and cognitive deficits, and extend to structural and other pathological features. We first consider the primary technological approaches to the generation of such mutants, to include their relative merits and demerits, and then highlight the diverse phenotypic approaches that have been developed for their assessment. The chapter then considers the application of mutant phenotypes to study pathobiological and pharmacological mechanisms thought to be relevant for schizophrenia, particularly in terms of dopaminergic and glutamatergic dysfunction, and to an increasing range of candidate susceptibility genes and copy number variants. Finally, we discuss several pertinent issues and challenges within the field which relate to both phenotypic evaluation and a growing appreciation of the functional genomics of schizophrenia and the involvement of gene × environment interactions.

Sesquiterpenes and a monoterpenoid with acetylcholinesterase (AchE) inhibitory activity from Valeriana officinalis var. latiofolia in vitro and in vivo

Acetylcholinesterase Inhibitor (AchEI) is the most extensive in all anti-dementia drugs. The extracts and isolated compounds from the Valeriana genus have shown anti-dementia bioactivity. Four new sesquiterpenoids (1-4) and a new monoterpenoid (5) were isolated from the root of Valeriana officinalis var. latiofolia. The acetylcholinesterase (AchE) inhibitory activity of isolates was evaluated by modified Ellman method in vitro. Learning and memory ability of compound 4 on mice was evaluated by the Morris water maze. The contents of acetylcholine (Ach), acetylcholine transferase (ChAT) and AchE in mice brains were determined by colorimetry. The results showed IC50 of compound 4 was 0.161 μM in vitro. Compared with the normal group, the learning and memory ability of mice and the contents of Ach and ChAT decreased in model group mice (P<0.01), while the AchE increased (P<0.01). Compared with the model group, Ach and ChAT in the positive control group, the high-dose group and the medium-dose group increased (P<0.01), while the AchE decreased (P<0.01). Compound 4 can improve the learning and memory abilities of APPswe/PSΔE9 double-transgenic mice, and the mechanism may be related to the regulation of the relative enzyme in the cholinergic system.

Dysbindin-1 modifies signaling and cellular localization of recombinant, human D₃ and D₂ receptors

Dystrobrevin binding protein-1 (dysbindin-1), a candidate gene for schizophrenia, modulates cognition, synaptic plasticity and frontocortical circuitry and interacts with glutamatergic and dopaminergic transmission. Loss of dysbindin-1 modifies cellular trafficking of dopamine (DA) D2 receptors to increase cell surface expression, but its influence upon signaling has never been characterized. Further, the effects of dysbindin-1 upon closely related D3 receptors remain unexplored. Hence, we examined the impact of dysbindin-1 (isoform A) co-expression on the localization and coupling of human D2L and D3 receptors stably expressed in Chinese hamster ovary or SH-SY5Y cells lacking endogenous dysbindin-1. Dysbindin-1 co-transfection decreased cell surface expression of both D3 and D2L receptors. Further, while their affinity for DA was unchanged, dysbindin-1 reduced the magnitude and potency of DA-induced adenylate cylase recruitment/cAMP production. Dysbindin-1 also blunted the amplitude of DA-induced phosphorylation of ERK1/2 and Akt at both D2L and D3 receptors without, in contrast to cAMP, affecting the potency of DA. Interference with calveolin/clathrin-mediated processes of internalization prevented the modification by dysbindin-1 of ERK1/2 and adenylyl cyclase stimulation at D2L and D3 receptors. Finally, underpinning the specificity of the influence of dysbindin-1 on D2L and D3 receptors, dysbindin-1 did not modify recruitment of adenylyl cyclase by D1 receptors. These observations demonstrate that dysbindin-1 influences cell surface expression of D3 in addition to D2L receptors, and that it modulates activation of their signaling pathways. Accordingly, both a deficiency and an excess of dysbindin-1 may be disruptive for dopaminergic transmission, supporting its link to schizophrenia and other CNS disorders. Dysbindin-1, a candidate gene for schizophrenia, alters D2 receptors cell surface expression. We demonstrate that dysbindin-1 expression also influences cell surface levels of D3 receptors. Further, Dysbindin-1 reduces DA-induced adenylate cylase recruitment/cAMP production and modifies major signaling pathways (Akt and extracellular signal-regulated kinases1/2 (ERK1/2)) of both D2 and D3 receptors. Dysbindin-1 modulates thus D2 and D3 receptor signaling, supporting a link to schizophrenia.

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.

Recognition deficits in mice carrying mutations of genes encoding BLOC-1 subunits pallidin or dysbindin

Numerous studies have implicated DTNBP1, the gene encoding dystrobrevin-binding protein or dysbindin, as a candidate risk gene for schizophrenia, though this relationship remains somewhat controversial. Variation in dysbindin, and its location on chromosome 6p, has been associated with cognitive processes, including those relying on a complex system of glutamatergic and dopaminergic interactions. Dysbindin is one of the seven protein subunits that comprise the biogenesis of lysosome-related organelles complex 1 (BLOC-1). Dysbindin protein levels are lower in mice with null mutations in pallidin, another gene in the BLOC-1, and pallidin levels are lower in mice with null mutations in the dysbindin gene, suggesting that multiple subunit proteins must be present to form a functional oligomeric complex. Furthermore, pallidin and dysbindin have similar distribution patterns in a mouse and human brain. Here, we investigated whether the apparent correspondence of pallid and dysbindin at the level of gene expression is also found at the level of behavior. Hypothesizing a mutation leading to underexpression of either of these proteins should show similar phenotypic effects, we studied recognition memory in both strains using the novel object recognition task (NORT) and social novelty recognition task (SNRT). We found that mice with a null mutation in either gene are impaired on SNRT and NORT when compared with wild-type controls. These results support the conclusion that deficits consistent with recognition memory impairment, a cognitive function that is impaired in schizophrenia, result from either pallidin or dysbindin mutations, possibly through degradation of BLOC-1 expression and/or function.

Src kinase as a mediator of convergent molecular abnormalities leading to NMDAR hypoactivity in schizophrenia

Numerous investigations support decreased glutamatergic signaling as a pathogenic mechanism of schizophrenia, yet the molecular underpinnings for such dysregulation are largely unknown. In the post-mortem dorsolateral prefrontal cortex (DLPFC), we found striking decreases in tyrosine phosphorylation of N-methyl-D aspartate (NMDA) receptor subunit 2 (GluN2) that is critical for neuroplasticity. The decreased GluN2 activity in schizophrenia may not be because of downregulation of NMDA receptors as MK-801 binding and NMDA receptor complexes in postsynaptic density (PSD) were in fact increased in schizophrenia cases. At the postreceptor level, however, we found striking reductions in the protein kinase C, Pyk 2 and Src kinase activity that in tandem can decrease GluN2 activation. Given that Src serves as a hub of various signaling mechanisms affecting GluN2 phosphorylation, we postulated that Src hypoactivity may result from convergent alterations of various schizophrenia susceptibility pathways and thus mediate their effects on NMDA receptor signaling. Indeed, the DLPFC of schizophrenia cases exhibit increased PSD-95 and erbB4 and decreased receptor-type tyrosine-protein phosphatase-α (RPTPα) and dysbindin-1, each of which reduces Src activity via protein interaction with Src. To test genomic underpinnings for Src hypoactivity, we examined genome-wide association study results, incorporating 13 394 cases and 34 676 controls. We found no significant association of individual variants of Src and its direct regulators with schizophrenia. However, a protein-protein interaction-based network centered on Src showed significant enrichment of gene-level associations with schizophrenia compared with other psychiatric illnesses. Our results together demonstrate striking decreases in NMDA receptor signaling at the postreceptor level and propose Src as a nodal point of convergent dysregulations affecting NMDA receptor pathway via protein-protein associations.

The Schizophrenia-Related Protein Dysbindin-1A Is Degraded and Facilitates NF-Kappa B Activity in the Nucleus

Dystrobrevin-binding protein 1 (DTNBP1), a gene encoding dysbindin-1, has been identified as a susceptibility gene for schizophrenia. Functioning with partners in synapses or the cytoplasm, this gene regulates neurite outgrowth and neurotransmitter release. Loss of dysbindin-1 affects schizophrenia pathology. Dysbindin-1 is also found in the nucleus, however, the characteristics of dysbindin in the nucleus are not fully understood. Here, we found that dysbindin-1A is degraded in the nucleus via the ubiquitin-proteasome system and that amino acids 2-41 at the N-terminus are required for this process. By interacting with p65, dysbindin-1A promotes the transcriptional activity of NF-kappa B in the nucleus and positively regulates MMP-9 expression. Taken together, the data obtained in this study demonstrate that dysbindin-1A protein levels are highly regulated in the nucleus and that dysbindin-1A regulates transcription factor NF-kappa B activity to promote the expression of MMP-9 and TNF-α.

MeCP2 in the rostral striatum maintains local dopamine content critical for psychomotor control

Methyl-CpG binding protein 2 (MeCP2) is a chromatin regulator highly expressed in mature neurons. Mutations of MECP2 gene cause >90% cases of Rett syndrome, a neurodevelopmental disorder featured by striking psychomotor dysfunction. In Mecp2-null mice, the motor deficits are associated with reduction of dopamine content in the striatum, the input nucleus of basal ganglia mostly composed of GABAergic neurons. Here we investigated the causal role of MeCP2 in modulation of striatal dopamine content and psychomotor function. We found that mice with selective removal of MeCP2 in forebrain GABAergic neurons, predominantly in the striatum, phenocopied Mecp2-null mice in dopamine deregulation and motor dysfunction. Selective expression of MeCP2 in the striatum preserved dopamine content and psychomotor function in both males and females. Notably, the dopamine deregulation was primarily confined to the rostral striatum, and focal deletion or reactivation of MeCP2 expression in the rostral striatum through adeno-associated virus effectively disrupted or restored dopamine content and locomotor activity, respectively. Together, these findings demonstrate that striatal MeCP2 maintains local dopamine content in a non-cell autonomous manner in the rostral striatum and that is critical for psychomotor control.

Loss of dysbindin-1, a risk gene for schizophrenia, leads to impaired group 1 metabotropic glutamate receptor function in mice

The expression of dysbindin-1, a protein coded by the risk gene dtnbp1, is reduced in the brains of schizophrenia patients. Evidence indicates a role of dysbindin-1 in dopaminergic and glutamatergic transmission. Glutamatergic transmission and plasticity at excitatory synapses is critically regulated by G-protein coupled metabotropic glutamate receptor (mGluR) family members, that have been implicated in schizophrenia. Here, we report a role of dysbindin-1 in hippocampal group 1 mGluR (mGluRI) function in mice. In hippocampal synaptoneurosomal preparations from sandy (sdy) mice, that have a loss of function mutation in dysbindin-1 gene, we observed a striking reduction in mGluRI agonist [(S)-3, 5-dihydroxyphenylglycine] (DHPG)-induced phosphorylation of extracellular signal regulated kinase 1/2 (ERK1/2). This mGluR-ERK1/2 deficit occurred in the absence of significant changes in protein levels of the two members of the mGluRI family (i.e., mGluR1 and mGluR5) or in another mGluRI signaling pathway, i.e., protein kinase C (PKC). Aberrant mGluRI-ERK1/2 signaling affected hippocampal synaptic plasticity in the sdy mutants as DHPG-induced long-term depression (LTD) at CA1 excitatory synapses was significantly reduced. Behavioral data suggest that the mGluRI hypofunction may underlie some of the cognitive abnormalities described in sdy mice as the administration of CDPPB (3-cyano-N-(1, 3-diphenyl-1H-pyrazol-5-yl benzamide), a positive allosteric modulator of mGluR5, rescued short-term object recognition and spatial learning and memory deficits in these mice. Taken together, our data suggest a novel role of dysbindin-1 in regulating mGluRI functions.

Behavioral characterization of mice overexpressing human dysbindin-1

Background

The dysbindin-1 gene (DTNBP1: dystrobrevin binding protein 1) is a promising schizophrenia susceptibility gene, known to localize almost exclusively to neurons in the brain, and participates in the regulation of neurotransmitter release, membrane-surface receptor expression, and synaptic plasticity. Sandy mice, with spontaneous Dtnbp1 deletion, display behavioral abnormalities relevant to symptoms of schizophrenia. However, it remains unknown if dysbindin-1 gain-of-function is beneficial or detrimental.

Results

To answer this question and gain further insight into the pathophysiology and therapeutic potential of dysbindin-1, we developed transgenic mice expressing human DTNBP1 (Dys1A-Tg) and analyzed their behavioral phenotypes. Dys1A-Tg mice were born viable in the expected Mendelian ratios, apparently normal and fertile. Primary screening of behavior and function showed a marginal change in limb grasping in Dys1A-Tg mice. In addition, Dys1A-Tg mice exhibited increased hyperlocomotion after methamphetamine injection. Transcriptomic analysis identified several up- and down-regulated genes, including the immediate-early genes Arc and Egr2, in the prefrontal cortex of Dys1A-Tg mice.

Conclusions

The present findings in Dys1A-Tg mice support the role of dysbindin-1 in psychiatric disorders. The fact that either overexpression (Dys1A-Tg) or underexpression (Sandy) of dysbindin-1 leads to behavioral alterations in mice highlights the functional importance of dysbindin-1 in vivo.

Disrupted-In-Schizophrenia-1 (DISC1) interactome and mental disorders: impact of mouse models

Disrupted-In-Schizophrenia-1 (DISC1) has captured much attention because it predisposes individuals to a wide range of mental illnesses. Notably, a number of genes encoding proteins interacting with DISC1 are also considered to be relevant risk factors of mental disorders. We reasoned that the understanding of DISC1-associated mental disorders in the context of network principles will help to address fundamental properties of DISC1 as a disease gene. Systematic integration of behavioural phenotypes of genetic mouse lines carrying perturbation in DISC1 interacting proteins would contribute to a better resolution of neurobiological mechanisms of mental disorders associated with the impaired DISC1 interactome and lead to a development of network medicine. This review also makes specific recommendations of how to assess DISC1 associated mental disorders in mouse models and discuss future directions.

Mutations in the BLOC-1 subunits dysbindin and muted generate divergent and dosage-dependent phenotypes

Post-mortem analysis has revealed reduced levels of the protein dysbindin in the brains of those suffering from the neurodevelopmental disorder schizophrenia. Consequently, mechanisms controlling the cellular levels of dysbindin and its interacting partners may participate in neurodevelopmental processes impaired in that disorder. To address this question, we studied loss of function mutations in the genes encoding dysbindin and its interacting BLOC-1 subunits. We focused on BLOC-1 mutants affecting synapse composition and function in addition to their established systemic pigmentation, hematological, and lung phenotypes. We tested phenotypic homogeneity and gene dosage effects in the mouse null alleles muted (Bloc1s5(mu/mu)) and dysbindin (Bloc1s8(sdy/sdy)). Transcripts of NMDA receptor subunits and GABAergic interneuron markers, as well as expression of BLOC-1 subunit gene products, were affected differently in the brains of Bloc1s5(mu/mu) and Bloc1s8(sdy/sdy) mice. Unlike Bloc1s8(sdy/sdy), elimination of one or two copies of Bloc1s5 generated indistinguishable pallidin transcript phenotypes. We conclude that monogenic mutations abrogating the expression of a protein complex subunit differentially affect the expression of other complex transcripts and polypeptides as well as their downstream effectors. We propose that the genetic disruption of different subunits of protein complexes and combinations thereof diversifies phenotypic presentation of pathway deficiencies, contributing to the wide phenotypic spectrum and complexity of neurodevelopmental disorders.

Epistatic interaction between COMT and DTNBP1 modulates prefrontal function in mice and in humans

Cognitive functions are highly heritable and the impact of complex genetic interactions, though undoubtedly important, has received little investigation. Here we show in an animal model and in a human neuroimaging experiment a consistent non-linear interaction between two genes--catechol-O-methyl transferase (COMT) and dysbindin (dys; dystrobrevin-binding protein 1 (DTNBP1))--implicated through different mechanisms in cortical dopamine signaling and prefrontal cognitive function. In mice, we found that a single genetic mutation reducing expression of either COMT or DTNBP1 alone produced working memory advantages, while, in dramatic contrast, genetic reduction of both in the same mouse produced working memory deficits. We found evidence of the same non-linear genetic interaction in prefrontal cortical function in humans. In healthy volunteers (N=176) studied with functional magnetic resonance imaging during a working memory paradigm, individuals homozygous for the COMT rs4680 Met allele that reduces COMT enzyme activity showed a relatively more efficient prefrontal engagement. In contrast, we found that the same genotype was less efficient on the background of a dys haplotype associated with decreased DTNBP1 expression. These results illustrate that epistasis can be functionally multi-directional and non-linear and that a putatively beneficial allele in one epistastic context is a relatively deleterious one in another. These data also have important implications for single-locus association analyses of complex traits.

CHRONIC NEONATAL DIAZOXIDE THERAPY IS NOT ASSOCIATED WITH ADVERSE EFFECTS

Diazoxide is an ATP-sensitive potassium channel (K_ATP) agonist that has been shown to neuroprotective effects. These observations raise the possibility that diazoxide may have potential as a therapeutic agent for other applications. This study investigated (1) the long term effects of chronic neonatal administration of diazoxide and (2) the role of K_ATP on murin behavior and neurohistology. C57B/6J pups were injected daily with diazoxide (10, 20 or 50 mg kg^-1) or vehicle from Postnatal days 2 (P2) through P12. Pups were allow to mature and underwent behavioral testing at 5-7 months of age. After behavioral testing, animals were euthanized and morphology of the brains was assessed. No long term adverse effects of neonatal diazoxide therapy on physical characteristics, visual acuity, sensori-motor reflexes, spontaneous locomotor activity, motor coordination/balance or motor learning and memory were observed. In addition, no morphological changes were observed on brains. However, we did observe that diazoxide therapy causes depressive-like phenotypes in female murine mice. Chronic neonatal diazoxide therapy does not cause deficits or enhancements in mice behavior. Diazoxide does not cause abnormal morphological changes in brain anatomy. However, diazoxide does cause gender specific depressive-like phenotype in mice.