Disturbed synaptic connectivity in schizophrenia: convergence of genetic risk factors during neurodevelopment

Epigenomic landscapes during prefrontal cortex development and aging in rhesus

The prefrontal cortex (PFC) is essential for higher-level cognitive functions. How epigenetic dynamics participates in PFC development and aging is largely unknown. Here, we profiled epigenomic landscapes of rhesus monkey PFCs from prenatal to aging stages. The dynamics of chromatin states, including higher-order chromatin structure, chromatin interaction and histone modifications are coordinated to regulate stage-specific gene transcription, participating in distinct processes of neurodevelopment. Dramatic changes of epigenetic signals occur around the birth stage. Notably, genes involved in neuronal cell differentiation and layer specification are pre-configured by bivalent promoters. We identified a cis-regulatory module and the transcription factors (TFs) associated with basal radial glia development, which was associated with large brain size in primates. These TFs include GLI3, CREB5 and SOX9. Interestingly, the genes associated with the basal radial glia (bRG)-associated cis-element module, such as SRY and SOX9, are enriched in sex differentiation. Schizophrenia-associated single nucleotide polymorphisms are more enriched in super enhancers (SEs) than typical enhancers, suggesting that SEs play an important role in neural network wiring. A cis-regulatory element of DBN1 is identified, which is critical for neuronal cell proliferation and synaptic neuron differentiation. Notably, the loss of distal chromatin interaction and H3K27me3 signal are hallmarks of PFC aging, which are associated with abnormal expression of aging-related genes and transposon activation, respectively. Collectively, our findings shed light on epigenetic mechanisms underlying primate brain development and aging.

Impact of Abl2/Arg deficiency on anxiety and depressive behaviors in mice

Abl2/Arg (ABL-related gene) is a member of the Abelson family of nonreceptor tyrosine kinases, known for its role in tumor progression, metastasis, tissue injury responses, inflammation, neural degeneration, and other diseases. In this study, we developed Abl2/Arg knockout (abl2-/-) mice to explore its impact on sensory/motor functions and emotion-related behaviors. Our findings show that abl2-/- mice exhibit normal growth and phenotypic characteristics, closely resembling their wild-type (WT) counterparts. Behavioral tests, including the elevated plus maze, marble-burying behavior test, and open field test, indicated pronounced anxiety-like behaviors in abl2-/- mice compared to WT mice. Furthermore, in the tail suspension test, abl2-/- mice showed a significant decrease in mobility time, suggesting depressive-like behavior. Conversely, in the Y-maze and cliff avoidance reaction tests, no notable differences were observed between abl2-/- and WT mice, suggesting the absence of working memory deficits and impulsivity in abl2-/- mice. Proteomic analysis of the hippocampus in abl2-/- mice highlighted significant alterations in proteins related to anxiety and depression, especially those associated with the GABAergic synapse in inhibitory neurotransmission. The expression of Gabbr2 was significantly reduced in the hippocampus of abl2-/- compared to WT mice, and intraperitoneal treatment of GABA receptor agonist Gaboxadol normalized anxiety/depression-related behaviors of abl2-/- mice. These findings underscore the potential role of Abl2/Arg in influencing anxiety and depressive-like behaviors, thereby contributing valuable insights into its broader physiological and pathological functions.

Morphological and transcriptomic analyses of stem cell-derived cortical neurons reveal mechanisms underlying synaptic dysfunction in schizophrenia

BACKGROUND

Postmortem studies in schizophrenia consistently show reduced dendritic spines in the cerebral cortex but the mechanistic underpinnings of these deficits remain unknown. Recent genome-wide association studies and exome sequencing investigations implicate synaptic genes and processes in the disease biology of schizophrenia.

METHODS

We generated human cortical pyramidal neurons by differentiating iPSCs of seven schizophrenia patients and seven healthy subjects, quantified dendritic spines and synapses in different cortical neuron subtypes, and carried out transcriptomic studies to identify differentially regulated genes and aberrant cellular processes in schizophrenia.

RESULTS

Cortical neurons expressing layer III marker CUX1, but not those expressing layer V marker CTIP2, showed significant reduction in dendritic spine density in schizophrenia, mirroring findings in postmortem studies. Transcriptomic experiments in iPSC-derived cortical neurons showed that differentially expressed genes in schizophrenia were enriched for genes implicated in schizophrenia in genome-wide association and exome sequencing studies. Moreover, most of the differentially expressed genes implicated in schizophrenia genetic studies had lower expression levels in schizophrenia cortical neurons. Network analysis of differentially expressed genes led to identification of NRXN3 as a hub gene, and follow-up experiments showed specific reduction of the NRXN3 204 isoform in schizophrenia neurons. Furthermore, overexpression of the NRXN3 204 isoform in schizophrenia neurons rescued the spine and synapse deficits in the cortical neurons while knockdown of NRXN3 204 in healthy neurons phenocopied spine and synapse deficits seen in schizophrenia cortical neurons. The antipsychotic clozapine increased expression of the NRXN3 204 isoform in schizophrenia cortical neurons and rescued the spine and synapse density deficits.

CONCLUSIONS

Taken together, our findings in iPSC-derived cortical neurons recapitulate cell type-specific findings in postmortem studies in schizophrenia and have led to the identification of a specific isoform of NRXN3 that modulates synaptic deficits in schizophrenia neurons.

Cortical and thalamic modulation of auditory gating in the posterior parietal cortex of awake mice

Auditory gating (AG) is an adaptive mechanism for filtering out redundant acoustic stimuli to protect the brain against information overload. AG deficits have been found in many mental illnesses, including schizophrenia (SZ). However, the neural correlates of AG remain poorly understood. Here, we found that the posterior parietal cortex (PPC) shows an intermediate level of AG in auditory thalamocortical circuits, with a laminar profile in which the strongest AG is in the granular layer. Furthermore, AG of the PPC was decreased and increased by optogenetic inactivation of the medial dorsal thalamic nucleus (MD) and auditory cortex (AC), respectively. Optogenetically activating the axons from the MD and AC drove neural activities in the PPC without an obvious AG. These results indicated that AG in the PPC is determined by the integrated signal streams from the MD and AC in a bottom-up manner. We also found that a mouse model of SZ (postnatal administration of noncompetitive N-methyl-d-aspartate receptor antagonist) presented an AG deficit in the PPC, which may be inherited from the dysfunction of MD. Together, our findings reveal a neural circuit underlying the generation of AG in the PPC and its involvement in the AG deficit of SZ.

Multiple Rare Risk Coding Variants in Postsynaptic Density-Related Genes Associated With Schizophrenia Susceptibility

Objective

Schizophrenia is a chronic debilitating neurobiological disorder of aberrant synaptic connectivity and synaptogenesis. Postsynaptic density (PSD)–related proteins in N-methyl-D-aspartate receptor–postsynaptic signaling complexes are crucial to regulating the synaptic transmission and functions of various synaptic receptors. This study examined the role of PSD-related genes in susceptibility to schizophrenia.

Methods

We resequenced 18 genes encoding the disks large-associated protein (DLGAP), HOMER, neuroligin (NLGN), neurexin, and SH3 and multiple ankyrin repeat domains (SHANK) protein families in 98 schizophrenic patients with family psychiatric history using semiconductor sequencing. We analyzed the protein function of the identified rare schizophrenia-associated mutants via immunoblotting and immunocytochemistry.

Results

We identified 50 missense heterozygous mutations in 98 schizophrenic patients with family psychiatric history, and in silico analysis revealed some as damaging or pathological to the protein function. Ten missense mutations were absent from the dbSNP database, the gnomAD (non-neuro) dataset, and 1,517 healthy controls from Taiwan BioBank. Immunoblotting revealed eight missense mutants with altered protein expressions in cultured cells compared with the wild type.

Conclusion

Our findings suggest that PSD-related genes, especially the NLGN, SHANK, and DLGAP families, harbor rare functional mutations that might alter protein expression in some patients with schizophrenia, supporting contributing rare coding variants into the genetic architecture of schizophrenia.

Progressive reduction of auditory evoked gamma in first episode schizophrenia but not clinical high risk individuals

The early auditory-evoked gamma band response (EAGBR) may serve as an index of the integrity of fast recurrent inhibition or synaptic connectivity in the auditory cortex, where abnormalities in individuals with schizophrenia have been consistently found. The EAGBR has been rarely investigated in first episode schizophrenia patients (FESZ) and individuals at clinical high risk (CHR) for schizophrenia, and never been compared directly between these populations nor evaluated longitudinally. Here we examined the EAGBR in FESZ, CHR, and matched healthy controls (HC) at baseline and 1-year follow-up assessments to determine whether the EAGBR was affected in these clinical groups, and whether any EAGBR abnormalities changed over time. The electroencephalogram was recorded with a dense electrode array while subjects (18 FESZ, 18 CHR, and 40 HC) performed an auditory oddball task. Event-related spectral measures (phase locking factor [PLF] and evoked power) were computed on Morlet-wavelet-transformed single epochs from the standard trials. At baseline, EAGBR PLF and evoked power did not differ between groups. FESZ showed progressive reductions of PLF and evoked power from baseline to follow-up, and deficits in PLF at follow-up compared to HC. EAGBR peak frequency also increased at temporal sites in FESZ from baseline to follow-up. Longitudinal effects on the EAGBR were not found in CHR or HC, nor did these groups differ at follow-up. In conclusion, we detected neurophysiological changes of auditory cortex function in FESZ during a one-year period, which were not observed in CHR. These findings are discussed within the context of neurodevelopmental models of schizophrenia.

Aspects of excitatory/inhibitory synapses in multiple brain regions are correlated with levels of brain-derived neurotrophic factor/neurotrophin-3

Appropriate synapse formation during development is necessary for normal brain function, and synapse impairment is often associated with brain dysfunction. Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) are key factors in regulating synaptic development. We previously reported that BDNF/NT-3 secretion was enhanced by calcium-dependent activator protein for secretion 2 (CADPS2). Although BDNF/NT-3 and CADPS2 are co-expressed in various brain regions, the effect of Cadps2-deficiency on brain region-specific BDNF/NT-3 levels and synaptic development remains elusive. Here, we show developmental changes of BDNF/NT-3 levels and we assess disruption of excitatory/inhibitory synapses in multiple brain regions (cerebellum, hypothalamus, striatum, hippocampus, parietal cortex and prefrontal cortex) of Cadps2 knockout (KO) mice compared with wild-type (WT) mice. Compared with WT, BDNF levels in KO mice were reduced in young/adult hippocampus, but increased in young hypothalamus, while NT-3 levels were reduced in adult cerebellum and young hippocampus, but increased in adult parietal cortex. Immunofluorescence of vGluT1, an excitatory synapse marker, and vGAT, an inhibitory synapse marker, in adult KO showed that vGluT1 was higher in the cerebellum and parietal cortex but lower in the hippocampus, whereas vGAT was lower in the hippocampus and parietal cortex compared with WT. Immunolabeling for both vGluT1 and vGAT was increased in the parietal cortex but vGAT was decreased in the cerebellum in adult KO compared with WT. These data suggest that CADPS2-mediated secretion of BDNF/NT-3 may be involved in development and maturation of synapses and in the balance between inhibitory and excitatory synapses.

Altered brain cannabinoid 1 receptor mRNA expression across postnatal development in the MAM model of schizophrenia

Altered cannabinoid 1 receptor (CB1R) expression has been reported in the brain of subjects with schizophrenia, a developmental mental illness that usually emerges in late adolescence/early adulthood. However, the developmental period at which changes in the CB1R expression appear in schizophrenia is unknown. To gain insight into this factor, we assessed the postnatal developmental trajectory of CB1R expression in the methylazoxymethanol (MAM) model of schizophrenia. Using in situ hybridization with film and grain analyses, CB1R messenger RNA (mRNA) levels were quantified in multiple brain regions, including the medial prefrontal cortex (mPFC), secondary motor cortex, dorsomedial and dorsolateral striatum, dorsal subregions and ventral subiculum of the hippocampus, of MAM-treated rats and normal controls at three developmental periods [juvenile - postnatal day (PD) 30; adolescence - PD45; and adulthood - PD85]. In all brain regions studied, CB1R mRNA levels were highest in juveniles and then decreased progressively toward adolescent and adult levels in control and MAM-treated rats. However, in MAM-treated rats, CB1R mRNA levels were lower in the mPFC at PD85 and higher in the dorsolateral striatum at PD45 and PD85 relative to controls. Cellular analyses confirmed the changes in CB1R mRNA expression in MAM-treated rats. These findings are in accordance with previous studies showing a decrease in the CB1R mRNA expression from juvenile period to adolescence to adulthood in cortical, striatal, and hippocampal regions. Additionally, similar to most of the schizophrenia-like signs observed in the MAM model, embryonic exposure to MAM leads to schizophrenia-related changes in CB1R mRNA expression that only emerge later in development.

Integrin activity in neuronal connectivity

The formation of correct synaptic structures and neuronal connections is paramount for normal brain development and a functioning adult brain. The integrin family of cell adhesion receptors and their ligands play essential roles in the control of several processes regulating neuronal connectivity - including neurite outgrowth, the formation and maintenance of synapses, and synaptic plasticity - that are affected in neurodevelopmental disorders, such as autism spectrum disorders (ASDs) and schizophrenia. Many ASD- and schizophrenia-associated genes are linked to alterations in the genetic code of integrins and associated signalling pathways. In non-neuronal cells, crosstalk between integrin-mediated adhesions and the actin cytoskeleton, and the regulation of integrin activity (affinity for extracellular ligands) are widely studied in healthy and pathological settings. In contrast, the roles of integrin-linked pathways in the central nervous system remains less well defined. In this Review, we will provide an overview of the known pathways that are regulated by integrin-ECM interaction in developing neurons and in adult brain. We will also describe recent advances in the identification of mechanisms that regulate integrin activity in neurons, and highlight the interesting emerging links between integrins and neurodevelopment.

Defects in Bioenergetic Coupling in Schizophrenia

Synaptic neurotransmission relies on maintenance of the synapse and meeting the energy demands of neurons. Defects in excitatory and inhibitory synapses have been implicated in schizophrenia, likely contributing to positive and negative symptoms as well as impaired cognition. Recently, accumulating evidence has suggested that bioenergetic systems, important in both synaptic function and cognition, are abnormal in psychiatric illnesses such as schizophrenia. Animal models of synaptic dysfunction demonstrated endophenotypes of schizophrenia as well as bioenergetic abnormalities. We report findings on the bioenergetic interplay of astrocytes and neurons and discuss how dysregulation of these pathways may contribute to the pathogenesis of schizophrenia, highlighting metabolic systems as important therapeutic targets.

The Communication Between the Immune and Nervous Systems: The Role of IL-1β in Synaptopathies

In the last 15 years, groundbreaking genetic progress has underlined a convergence onto coherent synaptic pathways for most psychiatric and neurodevelopmental disorders, which are now collectively called “synaptopathies.” However, the modest size of inheritance detected so far indicates a multifactorial etiology for these disorders, underlining the key contribution of environmental effects to them. Inflammation is known to influence the risk and/or severity of a variety of synaptopathies. In particular, pro-inflammatory cytokines, produced and released in the brain by activated astrocytes and microglia, may play a pivotal role in these pathologies. Although the link between immune system activation and defects in cognitive processes is nowadays clearly established, the knowledge of the molecular mechanisms by which inflammatory mediators specifically hit synaptic components implicated in synaptopathies is still in its infancy. This review summarizes recent evidence showing that the pro-inflammatory cytokine interleukin-1β (IL-1β) specifically targets synaptopathy molecular substrate, leading to memory defects and pathological processes. In particular, we describe three specific pathways through which IL-1β affects (1) synaptic maintenance/dendritic complexity, (2) spine morphology, and (3) the excitatory/inhibitory balance. We coin the term immune synaptopathies to identify this class of diseases.

Differential effects of social isolation in adolescent and adult mice on behavior and cortical gene expression

Intact function of the medial prefrontal cortex (mPFC) function relies on proper development of excitatory and inhibitory neuronal populations and on integral myelination processes. Social isolation (SI) affects behavior and brain circuitry in adulthood, but previous rodent studies typically induced prolonged (post-weaning) exposure and failed to directly compare between the effects of SI in adolescent and adulthood. Here, we assessed the impact of a 3-week SI period, starting in mid-adolescence (around the onset of puberty) or adulthood, on a wide range of behaviors in adult male mice. Additionally, we asked whether adolescent SI would differentially affect the expression of excitatory and inhibitory neuronal markers and myelin-related genes in mPFC. Our findings indicate that mid-adolescent or adult SI increase anxiogenic behavior and locomotor activity. However, SI in adolescence uniquely affects the response to the psychotomimetic drug amphetamine, social and novelty exploration and performance in reversal and attentional set shifting tasks. Furthermore, adolescent but not adult SI increased the expression of glutamate markers in the adult mPFC. Our results imply that adolescent social deprivation is detrimental for normal development and may be particularly relevant to the investigation of developmental psychopathology.

Olanzapine Prevents the PCP-induced Reduction in the Neurite Outgrowth of Prefrontal Cortical Neurons via NRG1

Accumulating evidence suggests that reducing neurite outgrowth and synaptic plasticity plays a critical role in the pathology of cognitive deficits in schizophrenia. The N-methyl-D-aspartate receptor antagonist phencyclidine (PCP) can induce symptoms of schizophrenia as well as reduce dendritic spine density and neurite growth. The antipsychotic drug olanzapine may improve these deficits. This study aimed to investigate: (1) if olanzapine prevents PCP-induced suppression of neurite outgrowth and synaptic protein expression; (2) if olanzapine affects the Akt-GSK3 signaling pathway; and (3) the role of neuregulin 1 (NRG1) in this process. Immunofluorescence revealed that PCP treatment for 24 hours reduces both neurite length (28.5%) and the number of neurite branches (35.6%) in primary prefrontal cortical neuron cultures. PCP reduced protein and mRNA expressions of synaptophysin (24.9% and 23.2%, respectively) and PSD95 (31.5% and 21.4%, respectively), and the protein expression of p-Akt (26.7%) and p-GSK3β (35.2%). Olanzapine co-treatment prevented these PCP-induced effects in normal neurons but not in neurons from NRG1-knockout mice. These results indicate that NRG1 mediates the preventive effects of olanzapine on the PCP-induced impairment of neurite outgrowth and synaptic protein expression. This study provides potential targets for interventions on improving the efficacy of olanzapine on preventing cognitive deficits in schizophrenia.

Synaptic activity: An emerging player in schizophrenia

Schizophrenia is a polygenic disorder with a complex etiology. While the genetic and molecular underpinnings of the disease are poorly understood, variations in genes encoding synaptic pathways are consistently implicated. Although its impact is still an open question, a deficit in synaptic activity provides an attractive model to explain the cognitive etiology of schizophrenia. Recent advances in high-throughput imaging and functional studies bring new hope for the application of in vitro disease modeling with patient-derived neurons to empirically ascertain the extent to which these synaptic pathways are involved in the disease. In addition, the emergent avenue of research targeted to probe neuronal connections is revealing critical insight into circuitry and may influence how we think about psychiatric disorders in the near future. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Schizophrenia and Depression Co-Morbidity: What We have Learned from Animal Models

Patients with schizophrenia are at an increased risk for the development of depression. Overlap in the symptoms and genetic risk factors between the two disorders suggests a common etiological mechanism may underlie the presentation of comorbid depression in schizophrenia. Understanding these shared mechanisms will be important in informing the development of new treatments. Rodent models are powerful tools for understanding gene function as it relates to behavior. Examining rodent models relevant to both schizophrenia and depression reveals a number of common mechanisms. Current models which demonstrate endophenotypes of both schizophrenia and depression are reviewed here, including models of CUB and SUSHI multiple domains 1, PDZ and LIM domain 5, glutamate Delta 1 receptor, diabetic db/db mice, neuropeptide Y, disrupted in schizophrenia 1, and its interacting partners, reelin, maternal immune activation, and social isolation. Neurotransmission, brain connectivity, the immune system, the environment, and metabolism emerge as potential common mechanisms linking these models and potentially explaining comorbid depression in schizophrenia.

Changes in the adolescent brain and the pathophysiology of psychotic disorders

Adolescence is a time of extensive neuroanatomical, functional, and chemical reorganisation of the brain which parallels substantial maturational changes in cognition and affect regulation. This period is characterised by stabilisation of synapses to diminish redundancy and increase efficiency of neural function, fine-tuning of excitatory and inhibitory neurotransmitter systems, beginning of integration between late maturing and early maturing brain structures, and development of effective connections. In effect, these so-called moving parts create a state of dynamic change that might underlie adolescent behaviours. Imbalances or changes in timing of these developmental processes clearly increase the risk for psychiatric disorders. Genetic, environmental, and epigenetic factors that shape brain development and hormonal changes that affect stress reactivity could be reasons why some, but not all, adolescents are at a heightened risk of developing a psychopathological disorder. In this Series paper, we assess the neurobiology of the changing adolescent brain, implications of this knowledge, and future research in major psychiatric disorders, particularly for psychotic disorders.

Pharmacological characterization of cultivated neuronal networks: relevance to synaptogenesis and synaptic connectivity

Mental disorders, such as schizophrenia or Alzheimer's disease, are associated with impaired synaptogenesis and/or synaptic communication. During development, neurons assemble into neuronal networks, the primary supracellular mediators of information processing. In addition to the orchestrated activation of genetic programs, spontaneous electrical activity and associated calcium signaling have been shown to be critically involved in the maturation of such neuronal networks. We established an in vitro model that recapitulates the maturation of neuronal networks, including spontaneous electrical activity. Upon plating, mouse primary hippocampal neurons grow neurites and interconnect via synapses to form a dish-wide neuronal network. Via live cell calcium imaging, we identified a limited period of time in which the spontaneous activity synchronizes across neurons, indicative of the formation of a functional network. After establishment of network activity, the neurons grow dendritic spines, the density of which was used as a morphological readout for neuronal maturity and connectivity. Hence, quantification of neurite outgrowth, synapse density, spontaneous neuronal activity, and dendritic spine density allowed to study neuronal network maturation from the day of plating until the presence of mature neuronal networks. Via acute pharmacological intervention, we show that synchronized network activity is mediated by the NMDA-R. The balance between kynurenic and quinolinic acid, both neuro-active intermediates in the tryptophan/kynurenine pathway, was shown to be decisive for the maintenance of network activity. Chronic modulation of the neurotrophic support influenced the network formation and revealed the extreme sensitivity of calcium imaging to detect subtle alterations in neuronal physiology. Given the reproducible cultivation in a 96-well setup in combination with fully automated analysis of the calcium recordings, this approach can be used to build a high-content screening assay usable for neurotoxicity screening, target identification/validation, or phenotypic drug screening.

Specific glial functions contribute to schizophrenia susceptibility

Schizophrenia is a highly polygenic brain disorder. The main hypothesis for disease etiology in schizophrenia primarily focuses on the role of dysfunctional synaptic transmission. Previous studies have therefore directed their investigations toward the role of neuronal dysfunction. However, recent studies have shown that apart from neurons, glial cells also play a major role in synaptic transmission. Therefore, we investigated the potential causal involvement of the 3 principle glial cell lineages in risk to schizophrenia. We performed a functional gene set analysis to test for the combined effects of genetic variants in glial type-specific genes for association with schizophrenia. We used genome-wide association data from the largest schizophrenia sample to date, including 13 689 cases and 18 226 healthy controls. Our results show that astrocyte and oligodendrocyte gene sets, but not microglia gene sets, are associated with an increased risk for schizophrenia. The astrocyte and oligodendrocyte findings are related to astrocyte signaling at the synapse, myelin membrane integrity, glial development, and epigenetic control. Together, these results show that genetic alterations underlying specific glial cell type functions increase susceptibility to schizophrenia and provide evidence that the neuronal hypothesis of schizophrenia should be extended to include the role of glia.

Peripheral biomarkers revisited: integrative profiling of peripheral samples for psychiatric research

Peripheral samples, such as blood and skin, have been used for decades in psychiatric research as surrogates for central nervous system samples. Although the validity of the data obtained from peripheral samples has been questioned and other state-of-the-art techniques, such as human brain imaging, genomics, and induced pluripotent stem cells, seem to reduce the value of peripheral cells, accumulating evidence has suggested that revisiting peripheral samples is worthwhile. Here, we re-evaluate the utility of peripheral samples and argue that establishing an understanding of the common signaling and biological processes in the brain and peripheral samples is required for the validity of such models. First, we present an overview of the available types of peripheral cells and describe their advantages and disadvantages. We then briefly summarize the main achievements of omics studies, including epigenome, transcriptome, proteome, and metabolome analyses, as well as the main findings of functional cellular assays, the results of which imply that alterations in neurotransmission, metabolism, the cell cycle, and the immune system may be partially responsible for the pathophysiology of major psychiatric disorders such as schizophrenia. Finally, we discuss the future utility of peripheral samples for the development of biomarkers and tailor-made therapies, such as multimodal assays that are used as a battery of disease and trait pathways and that might be potent and complimentary tools for use in psychiatric research.

PAKs inhibitors ameliorate schizophrenia-associated dendritic spine deterioration in vitro and in vivo during late adolescence

Drug discovery in psychiatry has been limited to chemical modifications of compounds originally discovered serendipitously. Therefore, more mechanism-oriented strategies of drug discovery for mental disorders are awaited. Schizophrenia is a devastating mental disorder with synaptic disconnectivity involved in its pathophysiology. Reduction in the dendritic spine density is a major alteration that has been reproducibly reported in the cerebral cortex of patients with schizophrenia. Disrupted-in-Schizophrenia-1 (DISC1), a factor that influences endophenotypes underlying schizophrenia and several other neuropsychiatric disorders, has a regulatory role in the postsynaptic density in association with the NMDA-type glutamate receptor, Kalirin-7, and Rac1. Prolonged knockdown of DISC1 leads to synaptic deterioration, reminiscent of the synaptic pathology of schizophrenia. Thus, we tested the effects of novel inhibitors to p21-activated kinases (PAKs), major targets of Rac1, on synaptic deterioration elicited by knockdown expression of DISC1. These compounds not only significantly ameliorated the synaptic deterioration triggered by DISC1 knockdown but also partially reversed the size of deteriorated synapses in culture. One of these PAK inhibitors prevented progressive synaptic deterioration in adolescence as shown by in vivo two-photon imaging and ameliorated a behavioral deficit in prepulse inhibition in adulthood in a DISC1 knockdown mouse model. The efficacy of PAK inhibitors may have implications in drug discovery for schizophrenia and related neuropsychiatric disorders in general.

Slitrk gene duplication and expression in the developing zebrafish nervous system

BACKGROUND

The Slitrk family of leucine-rich repeat (LRR) transmembrane proteins bears structural similarity to the Slits and the Trk receptor families, which exert well-established roles in directing nervous system development. Slitrks are less well understood, although they are highly expressed in the developing vertebrate nervous system. Moreover, slitrk variants are associated with several sensory and neuropsychiatric disorders, including myopia, deafness, obsessive-compulsive disorder (OCD), schizophrenia, and Tourette syndrome. Loss-of-function studies in mice show that Slitrks modulate neurite outgrowth and inhibitory synapse formation, although the molecular mechanisms of Slitrk function remain poorly characterized.

RESULTS

As a prelude to examining the functional roles of Slitrks, we identified eight slitrk orthologs in zebrafish and observed that seven of the eight orthologs were actively transcribed in the nervous system at embryonic, larval, and adult stages. Similar to previous findings in mice and humans, zebrafish slitrks exhibited unique but overlapping spatial and temporal expression patterns in the developing brain, retina, and spinal cord.

CONCLUSIONS

Zebrafish express Slitrks in the developing central nervous system at times and locations important to neuronal morphogenesis and synaptogenesis. Future studies will use zebrafish as a convenient, cost-effective model organism to characterize the functional roles of Slitrks in nervous system development.

Neurodevelopment in schizophrenia: the role of the wnt pathways

OBJECTIVES

To review the role of Wnt pathways in the neurodevelopment of schizophrenia.

METHODS

SYSTEMATIC PUBMED SEARCH, USING AS KEYWORDS ALL THE TERMS RELATED TO THE WNT PATHWAYS AND CROSSING THEM WITH EACH OF THE FOLLOWING AREAS: normal neurodevelopment and physiology, neurodevelopmental theory of schizophrenia, schizophrenia, and antipsychotic drug action.

RESULTS

Neurodevelopmental, behavioural, genetic, and psychopharmacological data point to the possible involvement of Wnt systems, especially the canonical pathway, in the pathophysiology of schizophrenia and in the mechanism of antipsychotic drug action. The molecules most consistently found to be associated with abnormalities or in antipsychotic drug action are Akt1, glycogen synthase kinase3beta, and beta-catenin. However, the extent to which they contribute to the pathophysiology of schizophrenia or to antipsychotic action remains to be established.

CONCLUSIONS

The study of the involvement of Wnt pathway abnormalities in schizophrenia may help in understanding this multifaceted clinical entity; the development of Wnt-related pharmacological targets must await the collection of more data.

Tardive dyskinesia in schizophrenia

Sarró et al report grey matter deficits associated with tardive dyskinesia in schizophrenia. Much evidence suggests that the intrinsic pathophysiology of schizophrenia contributes to predisposition to tardive dyskinesia. The possibility that antipsychotics might play a causal role in the grey matter deficits cannot be excluded, but the evidence is tenuous.

Altered fronto-limbic activity in children and adolescents with familial high risk for schizophrenia

Early symptoms of schizophrenia tend to emerge during adolescence, hich is a critical period for development of executive and emotional processing. While individuals with familial high risk (FHR) for schizophrenia may show cognitive and emotional changes, the neural mechanisms underlying the development of these changes remain unclear. The goal of this study was to identify functional differences in fronto-striato-limbic regions in children with FHR. Functional magnetic resonance imaging (MRI) data were collected from 21 children with a first-degree family member with schizophrenia and 21 controls without FHR. Participants performed an emotional oddball task requiring both selective attention and suppression of task-irrelevant emotional information. During selective attention, the group with FHR showed enhanced activation in the inferior frontal gyrus and caudate, with decreases in middle frontal gyrus and insular activation. The FHR group also showed greater age-related recruitment of anterior cingulate, temporal and occipital cortical areas during selective attention. During emotional processing, the FHR group showed decreased anterior cingulate activation, with decreased age-related recruitment of inferior frontal, parietal and occipital areas. The results suggest that FHR for schizophrenia may be associated with abnormal hyperactivation and hypoactivation of the neural circuitry engaged during executive and emotional processing and with age-related changes in neural recruitment during adolescence.

Quantitative systems pharmacology as an extension of PK/PD modeling in CNS research and development

Quantitative systems pharmacology (QSP) is a recent addition to the modeling and simulation toolbox for drug discovery and development and is based upon mathematical modeling of biophysical realistic biological processes in the disease area of interest. The combination of preclinical neurophysiology information with clinical data on pathology, imaging and clinical scales makes it a real translational tool. We will discuss the specific characteristics of QSP and where it differs from PK/PD modeling, such as the ability to provide support in target validation, clinical candidate selection and multi-target MedChem projects. In clinical development the approach can provide additional and unique evaluation of the effect of comedications, genotypes and disease states (patient populations) even before the initiation of actual trials. A powerful property is the ability to perform failure analysis. By giving examples from the CNS R&D field in schizophrenia and Alzheimer's disease, we will illustrate how this approach can make a difference for CNS R&D projects.

Synapse-specific contributions in the cortical pathology of schizophrenia

Schizophrenia (SZ) is often described as a disease of neuronal connectivity. Cognitive processes such as working memory, which are particularly dependent on the proper functioning of complex cortical circuitry, are disturbed in the disease. Reciprocal connections between pyramidal neurons and interneurons, as well as dopaminergic innervations, form the basis for higher cognition in the cortex. Nonetheless, only a few review articles are available which address how each synapse operates, and is possibly disturbed in SZ, at least in part by the mechanisms involving genetic susceptibility factors for SZ. In this review, we provide an overview of cortical glutamatergic, GABAergic, and dopaminergic circuitry, review SZ-associated deficits at each of these synapses, and discuss how genetic factors for SZ may contribute to SZ-related phenotype deficits in a synapse-specific manner. Pinpointing the spatially and temporally distinct sites of action of putative SZ susceptibility factors may help us better understand the pathological mechanisms of SZ, especially those associated with synaptic functioning and neuronal connectivity.

TCF4 (e2-2; ITF2): a schizophrenia-associated gene with pleiotropic effects on human disease

Common SNPs in the transcription factor 4 (TCF4; ITF2, E2-2, SEF-2) gene, which encodes a basic Helix-Loop-Helix (bHLH) transcription factor, are associated with schizophrenia, conferring a small increase in risk. Other common SNPs in the gene are associated with the common eye disorder Fuch's corneal dystrophy, while rare, mostly de novo inactivating mutations cause Pitt-Hopkins syndrome. In this review, we present a systematic bioinformatics and literature review of the genomics, biological function and interactome of TCF4 in the context of schizophrenia. The TCF4 gene is present in all vertebrates, and although protein length varies, there is high conservation of primary sequence, including the DNA binding domain. Humans have a unique leucine-rich nuclear export signal. There are two main isoforms (A and B), as well as complex splicing generating many possible N-terminal amino acid sequences. TCF4 is highly expressed in the brain, where plays a role in neurodevelopment, interacting with class II bHLH transcription factors Math1, HASH1, and neuroD2. The Ca(2+) sensor protein calmodulin interacts with the DNA binding domain of TCF4, inhibiting transcriptional activation. It is also the target of microRNAs, including mir137, which is implicated in schizophrenia. The schizophrenia-associated SNPs are in linkage disequilibrium with common variants within putative DNA regulatory elements, suggesting that regulation of expression may underlie association with schizophrenia. Combined gene co-expression analyses and curated protein-protein interaction data provide a network involving TCF4 and other putative schizophrenia susceptibility genes. These findings suggest new opportunities for understanding the molecular basis of schizophrenia and other mental disorders.

Systems biology, bioinformatics, and biomarkers in neuropsychiatry

Although neuropsychiatric (NP) disorders are among the top causes of disability worldwide with enormous financial costs, they can still be viewed as part of the most complex disorders that are of unknown etiology and incomprehensible pathophysiology. The complexity of NP disorders arises from their etiologic heterogeneity and the concurrent influence of environmental and genetic factors. In addition, the absence of rigid boundaries between the normal and diseased state, the remarkable overlap of symptoms among conditions, the high inter-individual and inter-population variations, and the absence of discriminative molecular and/or imaging biomarkers for these diseases makes difficult an accurate diagnosis. Along with the complexity of NP disorders, the practice of psychiatry suffers from a "top-down" method that relied on symptom checklists. Although checklist diagnoses cost less in terms of time and money, they are less accurate than a comprehensive assessment. Thus, reliable and objective diagnostic tools such as biomarkers are needed that can detect and discriminate among NP disorders. The real promise in understanding the pathophysiology of NP disorders lies in bringing back psychiatry to its biological basis in a systemic approach which is needed given the NP disorders' complexity to understand their normal functioning and response to perturbation. This approach is implemented in the systems biology discipline that enables the discovery of disease-specific NP biomarkers for diagnosis and therapeutics. Systems biology involves the use of sophisticated computer software "omics"-based discovery tools and advanced performance computational techniques in order to understand the behavior of biological systems and identify diagnostic and prognostic biomarkers specific for NP disorders together with new targets of therapeutics. In this review, we try to shed light on the need of systems biology, bioinformatics, and biomarkers in neuropsychiatry, and illustrate how the knowledge gained through these methodologies can be translated into clinical use providing clinicians with improved ability to diagnose, manage, and treat NP patients.

Genetics of schizophrenia from a clinicial perspective

Schizophrenia (SZ) is a common disorder that runs in families. It has a relatively high heritability, i.e., inherited factors account for the major proportion of its etiology. The high heritability has motivated gene mapping studies that have improved in sophistication through the past two decades. Belying earlier expectations, it is now becoming increasingly clear that the cause of SZ does not reside in a single mutation, or even in a single gene. Rather, there are multiple DNA variants, not all of which have been identified. Additional risk may be conferred by interactions between individual DNA variants, as well as 'gene-environment' interactions. We review studies that have accounted for a fraction of the heritability. Their relevance to the practising clinician is discussed. We propose that continuing research in DNA variation, in conjunction with rapid ongoing advances in allied fields, will yield dividends from the perspective of diagnosis, treatment prediction through pharmacogenetics, and rational treatment through discoveries in pathogenesis.

Functional gene group analysis identifies synaptic gene groups as risk factor for schizophrenia

Schizophrenia is a highly heritable disorder with a polygenic pattern of inheritance and a population prevalence of ~1%. Previous studies have implicated synaptic dysfunction in schizophrenia. We tested the accumulated association of genetic variants in expert-curated synaptic gene groups with schizophrenia in 4673 cases and 4965 healthy controls, using functional gene group analysis. Identifying groups of genes with similar cellular function rather than genes in isolation may have clinical implications for finding additional drug targets. We found that a group of 1026 synaptic genes was significantly associated with the risk of schizophrenia (P=7.6 × 10(-11)) and more strongly associated than 100 randomly drawn, matched control groups of genetic variants (P<0.01). Subsequent analysis of synaptic subgroups suggested that the strongest association signals are derived from three synaptic gene groups: intracellular signal transduction (P=2.0 × 10(-4)), excitability (P=9.0 × 10(-4)) and cell adhesion and trans-synaptic signaling (P=2.4 × 10(-3)). These results are consistent with a role of synaptic dysfunction in schizophrenia and imply that impaired intracellular signal transduction in synapses, synaptic excitability and cell adhesion and trans-synaptic signaling play a role in the pathology of schizophrenia.

Neurodevelopmental and neuropsychiatric behaviour defects arise from 14-3-3ζ deficiency

Complex neuropsychiatric disorders are believed to arise from multiple synergistic deficiencies within connected biological networks controlling neuronal migration, axonal pathfinding and synapse formation. Here, we show that deletion of 14-3-3ζ causes neurodevelopmental anomalies similar to those seen in neuropsychiatric disorders such as schizophrenia, autism spectrum disorder and bipolar disorder. 14-3-3ζ-deficient mice displayed striking behavioural and cognitive deficiencies including a reduced capacity to learn and remember, hyperactivity and disrupted sensorimotor gating. These deficits are accompanied by subtle developmental abnormalities of the hippocampus that are underpinned by aberrant neuronal migration. Significantly, 14-3-3ζ-deficient mice exhibited abnormal mossy fibre navigation and glutamatergic synapse formation. The molecular basis of these defects involves the schizophrenia risk factor, DISC1, which interacts isoform specifically with 14-3-3ζ. Our data provide the first evidence of a direct role for 14-3-3ζ deficiency in the aetiology of neurodevelopmental disorders and identifies 14-3-3ζ as a central risk factor in the schizophrenia protein interaction network.

Following the genes: a framework for animal modeling of psychiatric disorders

The number of individual cases of psychiatric disorders that can be ascribed to identified, rare, single mutations is increasing with great rapidity. Such mutations can be recapitulated in mice to generate animal models with direct etiological validity. Defining the underlying pathogenic mechanisms will require an experimental and theoretical framework to make the links from mutation to altered behavior in an animal or psychopathology in a human. Here, we discuss key elements of such a framework, including cell type-based phenotyping, developmental trajectories, linking circuit properties at micro and macro scales and definition of neurobiological phenotypes that are directly translatable to humans.

Taking a bird’s eye view on a mouse model review: a comparison of findings from mouse models targeting DISC1 or DISC1-interacting proteins

DISC1 has garnered much interest from researchers trying to understand the neurobiology of psychiatric disease. DISC1 appears to function as a structural protein hub for a number of molecules, many of which are considered disease-relevant targets in their own right. Thus, in this article, we compare behavioral, anatomical and biochemical findings in genetic mouse models of DISC1 and DISC1-interacting proteins to better understand how dysfunction of DISC1 and/or its interactors could contribute to psychiatric pathophysiology through convergent effects on distinct cells, circuits and behaviors. Consistencies in phenotypes across mouse models suggest that DISC1 and its binding partners are particularly critical for working memory performance, proper neuronal migration and cortical volume, normal spine density, an intact monoaminergic system, proper levels of parvalbumin and normal cytokine/stress signaling in the rodent. If these DISC1 functions translate to humans, it would explain how alterations in DISC1 or DISC1 interactors could contribute to psychiatric pathophysiology. Identification of such a biological convergence will hopefully improve the development of novel therapeutics for patients by focusing efforts on specific domains that are affected by DISC1-related genetic risk architecture.

Progress in defining the biological causes of schizophrenia

Schizophrenia is a common mental illness resulting from a complex interplay of genetic and environmental risk factors. Establishing its primary molecular and cellular aetiopathologies has proved difficult. However, this is a vital step towards the rational development of useful disease biomarkers and new therapeutic strategies. The advent and large-scale application of genomic, transcriptomic, proteomic and metabolomic technologies are generating data sets required to achieve this goal. This discovery phase, typified by its objective and hypothesis-free approach, is described in the first part of the review. The accumulating biological information, when viewed as a whole, reveals a number of biological process and subcellular locations that contribute to schizophrenia causation. The data also show that each technique targets different aspects of central nervous system function in the disease state. In the second part of the review, key schizophrenia candidate genes are discussed more fully. Two higher-order processes - adult neurogenesis and inflammation - that appear to have pathological relevance are also described in detail. Finally, three areas where progress would have a large impact on schizophrenia biology are discussed: deducing the causes of schizophrenia in the individual, explaining the phenomenon of cross-disorder risk factors, and distinguishing causative disease factors from those that are reactive or compensatory.

Readdressing synaptic pruning theory for schizophrenia: Combination of brain imaging and cell biology

Disturbance in the synapse has been suggested in the pathology of schizophrenia, especially through examination of autopsied brains from patients with the disease. Nonetheless, it has been unclear whether and how such disturbance is associated with the onset and progression of the disease in young adulthood. Some studies with magnetic resonance spectroscopy (MRS) have suggested that overpruning of dendritic spines may occur in the prodromal and early stages of schizophrenia. In addition, our recent study indicates that DISC1, a promising risk factor for schizophrenia, has a crucial role in the maintenance of the dendritic spine in association with activation of the NMDA-type glutamate receptor.1 Disturbance of spine maintenance can be linked to aberrant synaptic pruning during postnatal brain maturation. Biological studies with genetic models may provide us with an opportunity to validate experimentally the synaptic pruning theory for schizophrenia. An integrative strategy of brain imaging and cell biology may be a promising approach to address a key biological question for mental illnesses.

Glutamate signaling in the pathophysiology and therapy of schizophrenia

Glutamatergic neurotransmission, particularly through the N-methyl-d-aspartate (NMDA) receptor, has drawn attention for its role in the pathophysiology of schizophrenia. This paper reviews the neurodevelopmental origin and genetic susceptibility of schizophrenia relevant to NMDA neurotransmission, and discusses the relationship between NMDA hypofunction and different domains of symptom in schizophrenia as well as putative treatment modality for the disorder. A series of clinical trials and a meta-analysis which compared currently available NMDA-enhancing agents suggests that glycine, d-serine, and sarcosine are more efficacious than d-cycloserine in improving the overall psychopathology of schizophrenia without side effect or safety concern. In addition, enhancing glutamatergic neurotransmission via activating the AMPA receptor, metabotropic glutamate receptor or inhibition of d-amino acid oxidase (DAO) is also reviewed. More studies are needed to determine the NMDA vulnerability in schizophrenia and to confirm the long-term efficacy, functional outcome, and safety of these NMDA-enhancing agents in schizophrenic patients, particularly those with refractory negative and cognitive symptoms, or serious adverse effects while taking the existing antipsychotic agents.

Lack of change in markers of presynaptic terminal abundance alongside subtle reductions in markers of presynaptic terminal plasticity in prefrontal cortex of schizophrenia patients

BACKGROUND

Reduced synaptic connectivity in frontal cortex may contribute to schizophrenia symptoms. While altered messenger RNA (mRNA) and protein expression of various synaptic genes have been found, discrepancies between studies mean a generalizable synaptic pathology has not been identified.

METHODS

We determined if mRNAs encoding presynaptic proteins enriched in inhibitory (vesicular gamma-aminobutyric acid transporter [VGAT] and complexin 1) and/or excitatory (vesicular glutamate transporter 1 [VGluT1] and complexin 2) terminals are altered in the dorsolateral prefrontal cortex of subjects with schizophrenia (n = 37 patients, n = 37 control subjects). We also measured mRNA expression of markers associated with synaptic plasticity/neurite outgrowth (growth associated protein 43 [GAP43] and neuronal navigators [NAVs] 1 and 2) and mRNAs of other synaptic-associated proteins previously implicated in schizophrenia: dysbindin and vesicle-associated membrane protein 1 (VAMP1) mRNAs using quantitative polymerase chain reaction.

RESULTS

No significant changes in complexin 1, VGAT, complexin 2, VGluT1, dysbindin, NAV2, or VAMP1 mRNA expression were found; however, expression of mRNAs associated with plasticity/cytoskeletal modification (GAP43 and NAV1) was reduced in schizophrenia. Although dysbindin mRNA did not differ in schizophrenia compared with control subjects, dysbindin mRNA positively correlated with GAP43 and NAV1 in schizophrenia but not in control subjects, suggesting low levels of dysbindin may be linked to reduced plasticity in the disease state. No relationships between three dysbindin genetic polymorphisms previously associated with dysbindin mRNA levels were found.

CONCLUSIONS

A reduction in the plasticity of synaptic terminals supports the hypothesis that their reduced modifiability may contribute to neuropathology and working memory deficits in schizophrenia.