Dysfunction of mitochondria and GABAergic interneurons in the anterior cingulate cortex of individuals with schizophrenia

Here we re-analyze RNA-sequencing data from the anterior cingulate cortex (ACC) of SZ patients using recent methods to improve accuracy and sensitivity of results, such as the quality surrogate variable analysis (qSVA) method and the derfinder R package. We found that genes significantly down-regulated in SZ demonstrated an enrichment for parvalbumin-positive interneurons (FDR < 0.0001). Down-regulated genes were also enriched in oxidative phosphorylation functions (FDR < 0.05). We also addressed whether lifetime exposure to antipsychotics might influence gene expression, highlighting DUSP6, LBH, and NR1D1. Our results support the role of redox imbalance/mitochondrial dysfunction and implicate interneuron subtypes in SZ pathophysiology.

Anterior Insula-Associated Social Novelty Recognition: Pivotal Roles of a Local Retinoic Acid Cascade and Oxytocin Signaling

OBJECTIVE

Deficits in social cognition consistently underlie functional disabilities in a wide range of psychiatric disorders. Neuroimaging studies have suggested that the anterior insula is a "common core" brain region that is impaired across neurological and psychiatric disorders, which include social cognition deficits. Nevertheless, neurobiological mechanisms of the anterior insula for social cognition remain elusive. This study aims to fill this knowledge gap.

METHODS

To determine the role of the anterior insula in social cognition, the authors manipulated expression of Cyp26B1, an anterior insula-enriched molecule that is crucial for retinoic acid degradation and is involved in the pathology of neuropsychiatric conditions. Social cognition was mainly assayed using the three-chamber social interaction test. Multimodal analyses were conducted at the molecular, cellular, circuitry, and behavioral levels.

RESULTS

At the molecular and cellular level, anterior insula-mediated social novelty recognition is maintained by proper activity of the layer 5 pyramidal neurons, for which retinoic acid-mediated gene transcription can play a role. The authors also demonstrate that oxytocin influences the anterior insula-mediated social novelty recognition, although not by direct projection of oxytocin neurons, nor by direct diffusion of oxytocin to the anterior insula, which contrasts with the modes of oxytocin regulation onto the posterior insula. Instead, oxytocin affects oxytocin receptor-expressing neurons in the dorsal raphe nucleus, where serotonergic neurons are projected to the anterior insula. Furthermore, the authors show that serotonin 5-HT_2C receptor expressed in the anterior insula influences social novelty recognition.

CONCLUSIONS

The anterior insula plays a pivotal role in social novelty recognition that is partly regulated by a local retinoic acid cascade but also remotely regulated by oxytocin via a long-range circuit mechanism.

The transcriptome landscape associated with Disrupted-in-Schizophrenia-1 locus impairment in early development and adulthood

DISC1 was originally expected to be a genetic risk factor for schizophrenia, but the genome wide association studies have not supported this idea. In contrast, neurobiological studies of DISC1 in cell and animal models have demonstrated that direct perturbation of DISC1 protein elicits neurobiological and behavioral abnormalities relevant to a wide range of psychiatric conditions, in particular psychosis. Thus, the utility of DISC1 as a biological lead for psychosis research is clear. In the present study, we aimed to capture changes in the molecular landscape in the prefrontal cortex upon perturbation of DISC1, using the Disc1 locus impairment (Disc1-LI) model in which the majority of Disc1 isoforms have been depleted, and to explore potential molecular mediators relevant to psychiatric conditions. We observed a robust change in gene expression profile elicited by Disc1-LI in which the stronger effects on molecular networks were observed in early stage compared with those in adulthood. Significant alterations were found in specific pathways relevant to psychiatric conditions, such as pathways of signaling by G protein-coupled receptor, neurotransmitter release cycle, and voltage gated potassium channels. The differentially expressed genes (DEGs) between Disc1-LI and wild-type mice are significantly enriched not only in neurons, but also in astrocytes and oligodendrocyte precursor cells. The brain-disorder-associated genes at the mRNA and protein levels rather than those at the genomic levels are enriched in the DEGs. Together, our present study supports the utility of Disc1-LI mice in biological research for psychiatric disorder-associated molecular networks.

Translocator protein (TSPO) and stress cascades in mouse models of psychosis with inflammatory disturbances

Changes in inflammatory cascades have been implicated in the underlying pathophysiology of psychosis. Translocator protein 18 kDa (TSPO) has been used to assess neuroinflammatory processes in psychotic disorders. Nonetheless, it is unclear whether TSPO, a mitochondrial protein, can be interpreted as a general marker for inflammation in diseases involving psychosis. To address this question, we investigated TSPO signaling in representative mouse models for psychosis with inflammatory disturbances. The maternal immune activation and cuprizone short-term exposure models show different TSPO signaling. Furthermore, we observed similarities and differences in their respective stress pathways including stress hormone signaling and oxidative stress that are functionally interconnected with the inflammatory responses. We propose that more careful studies of TSPO distribution in neuroinflammation and other stress cascades associated with psychotic symptoms will allow us to understand the biological mechanisms underlying psychosis-related behaviors.

Overexpression of Neuregulin 1 Type III Confers Hippocampal mRNA Alterations and Schizophrenia-Like Behaviors in Mice

Neuregulin 1 (NRG1) is a schizophrenia candidate gene whose protein product is involved in neuronal migration, survival, and synaptic plasticity via production of specific isoforms. Importantly, NRG1 type III (NRG1 III) mRNA is increased in humans inheriting a schizophrenia risk haplotype for the NRG1 gene (HapICE), and NRG1 protein levels can be elevated in schizophrenia. The nature by which NRG1 type III overexpression results in schizophrenia-like behavior and brain pathology remains unclear, therefore we constructed a transgenic mouse with Nrg1 III overexpression in forebrain neurons (CamKII kinase+). Here, we demonstrate construct validity for this mouse model, as juvenile and adult Nrg1 III transgenic mice exhibit an overexpression of Nrg1 III mRNA and Nrg1 protein in multiple brain regions. Furthermore, Nrg1 III transgenic mice have face validity as they exhibit schizophrenia-relevant behavioral phenotypes including deficits in social preference, impaired fear-associated memory, and reduced prepulse inhibition. Additionally, microarray assay of hippocampal mRNA uncovered transcriptional alterations downstream of Nrg1 III overexpression, including changes in serotonin receptor 2C and angiotensin-converting enzyme. Transgenic mice did not exhibit other schizophrenia-relevant behaviors including hyperactivity, social withdrawal, or an increased vulnerability to the effects of MK-801 malate. Our results indicate that this novel Nrg1 III mouse is valid for modeling potential pathological mechanisms of some schizophrenia-like behaviors, for determining what other neurobiological changes may be downstream of elevated NRG1 III levels and for preclinically testing therapeutic strategies that may be specifically efficacious in patients with the NRG1 (HapICE) risk genotype.

Early-life decline in neurogenesis markers and age-related changes of TrkB splice variant expression in the human subependymal zone

Neurogenesis in the subependymal zone (SEZ) declines across the human lifespan, and reduced local neurotrophic support is speculated to be a contributing factor. While tyrosine receptor kinase B (TrkB) signalling is critical for neuronal differentiation, maturation and survival, little is known about subependymal TrkB expression changes during postnatal human life. In this study, we used quantitative PCR and in situ hybridisation to determine expression of the cell proliferation marker Ki67, the immature neuron marker doublecortin (DCX) and both full-length (TrkB-TK+) and truncated TrkB receptors (TrkB-TK-) in the human SEZ from infancy to middle age (n = 26-35, 41 days to 43 years). We further measured TrkB-TK+ and TrkB-TK- mRNAs in the SEZ from young adulthood into ageing (n = 50, 21-103 years), and related their transcript levels to neurogenic and glial cell markers. Ki67, DCX and both TrkB splice variant mRNAs significantly decreased in the SEZ from infancy to middle age. In contrast, TrkB-TK- mRNA increased in the SEZ from young adulthood into ageing, whereas TrkB-TK+ mRNA remained stable. TrkB-TK- mRNA positively correlated with expression of neural precursor (glial fibrillary acidic protein delta and achaete-scute homolog 1) and glial cell markers (vimentin and pan glial fibrillary acidic protein). TrkB-TK+ mRNA positively correlated with expression of neuronal cell markers (DCX and tubulin beta 3 class III). Our results indicate that cells residing in the human SEZ maintain their responsiveness to neurotrophins; however, this capability may change across postnatal life. We suggest that TrkB splice variants may differentially influence neuronal and glial differentiation in the human SEZ.

Valley of death: A proposal to build a "translational bridge" for the next generation

There is a great need for novel drug discovery for major mental illnesses, but multiple levels of challenges exist in both academia and industry, spanning from scientific understanding and institutional infrastructure to business risk and feasibility. The "valley of death," the large gap between basic scientific research and translation to novel therapeutics, underscores the need to restructure education and academic research to cultivate the fertile interface between academia and industry. In this opinion piece, we propose strategies to educate young trainees in the process of drug discovery and development, and prepare them for careers across this spectrum. In addition, we describe a research framework that considers the disease trajectory and underlying biology of mental disorders, which will help to address the core pathophysiology in novel treatments, and may even allow early detection and intervention. We hope that these changes will increase understanding among academia, industry, and government, which will ultimately improve the diagnosis, prognosis and treatment of mental disorders.

Molecular signatures associated with cognitive deficits in schizophrenia: a study of biopsied olfactory neural epithelium

Cognitive impairment is a key feature of schizophrenia (SZ) and determines functional outcome. Nonetheless, molecular signatures in neuronal tissues that associate with deficits are not well understood. We conducted nasal biopsy to obtain olfactory epithelium from patients with SZ and control subjects. The neural layers from the biopsied epithelium were enriched by laser-captured microdissection. We then performed an unbiased microarray expression study and implemented a systematic neuropsychological assessment on the same participants. The differentially regulated genes in SZ were further filtered based on correlation with neuropsychological traits. This strategy identified the SMAD 5 gene, and real-time quantitative PCR analysis also supports downregulation of the SMAD pathway in SZ. The SMAD pathway has been important in multiple tissues, including the role for neurodevelopment and bone formation. Here the involvement of the pathway in adult brain function is suggested. This exploratory study establishes a strategy to better identify neuronal molecular signatures that are potentially associated with mental illness and cognitive deficits. We propose that the SMAD pathway may be a novel target in addressing cognitive deficit of SZ in future studies.

Dimensional assessment of behavioral changes in the cuprizone short-term exposure model for psychosis

Recent clinical studies have suggested a role for immune/inflammatory responses in the pathophysiology of psychosis. However, a mechanistic understanding of this process and its application for drug discovery is underdeveloped. Here we assessed our recently developed cuprizone short-term exposure (CSE) mouse model across behavioral domains targeting neurocognitive and neuroaffective systems. We propose that the CSE model may be useful for understanding the mechanism associating inflammation and psychosis, with applications for drug discovery in that context.

Clinical utility of neuronal cells directly converted from fibroblasts of patients for neuropsychiatric disorders: studies of lysosomal storage diseases and channelopathy

Methodologies for generating functional neuronal cells directly from human fibroblasts [induced neuronal (iN) cells] have been recently developed, but the research so far has only focused on technical refinements or recapitulation of known pathological phenotypes. A critical question is whether this novel technology will contribute to elucidation of novel disease mechanisms or evaluation of therapeutic strategies. Here we have addressed this question by studying Tay-Sachs disease, a representative lysosomal storage disease, and Dravet syndrome, a form of severe myoclonic epilepsy in infancy, using human iN cells with feature of immature postmitotic glutamatergic neuronal cells. In Tay-Sachs disease, we have successfully characterized canonical neuronal pathology, massive accumulation of GM2 ganglioside, and demonstrated the suitability of this novel cell culture for future drug screening. In Dravet syndrome, we have identified a novel functional phenotype that was not suggested by studies of classical mouse models and human autopsied brains. Taken together, the present study demonstrates that human iN cells are useful for translational neuroscience research to explore novel disease mechanisms and evaluate therapeutic compounds. In the future, research using human iN cells with well-characterized genomic landscape can be integrated into multidisciplinary patient-oriented research on neuropsychiatric disorders to address novel disease mechanisms and evaluate therapeutic strategies.

Enhanced conversion of induced neuronal cells (iN cells) from human fibroblasts: Utility in uncovering cellular deficits in mental illness-associated chromosomal abnormalities

The novel technology of induced neuronal cells (iN cells) is promising for translational neuroscience, as it allows the conversion of human fibroblasts into cells with postmitotic neuronal traits. However, a major technical barrier is the low conversion rate. To overcome this problem, we optimized the conversion media. Using our improved formulation, we studied how major mental illness-associated chromosomal abnormalities may impact the characteristics of iN cells. We demonstrated that our new iN cell culture protocol enabled us to obtain more precise measurement of neuronal cellular phenotypes than previous iN cell methods. Thus, this iN cell culture provides a platform to efficiently obtain possible cellular phenotypes caused by genetic differences, which can be more thoroughly studied in research using other human cell models such as induced pluripotent stem cells.

Unique pharmacological actions of atypical neuroleptic quetiapine: possible role in cell cycle/fate control

Quetiapine is an atypical neuroleptic with a pharmacological profile distinct from classic neuroleptics that function primarily via blockade of dopamine D2 receptors. In the United States, quetiapine is currently approved for treating patients with schizophrenia, major depression and bipolar I disorder. Despite its widespread use, its cellular effects remain elusive. To address possible mechanisms, we chronically treated mice with quetiapine, haloperidol or vehicle and examined quetiapine-specific gene expression change in the frontal cortex. Through microarray analysis, we observed that several groups of genes were differentially expressed upon exposure to quetiapine compared with haloperidol or vehicle; among them, Cdkn1a, the gene encoding p21, exhibited the greatest fold change relative to haloperidol. The quetiapine-induced downregulation of p21/Cdkn1a was confirmed by real-time polymerase chain reaction and in situ hybridization. Consistent with single gene-level analyses, functional group analyses also indicated that gene sets associated with cell cycle/fate were differentially regulated in the quetiapine-treated group. In cortical cell cultures treated with quetiapine, p21/Cdkn1a was significantly downregulated in oligodendrocyte precursor cells and neurons, but not in astrocytes. We propose that cell cycle-associated intervention by quetiapine in the frontal cortex may underlie a unique efficacy of quetiapine compared with typical neuroleptics.