The cerebral microvasculature in schizophrenia: a laser capture microdissection study

Identification of important gene signatures in schizophrenia through feature fusion and genetic algorithm

Schizophrenia is a debilitating psychiatric disorder that can significantly affect a patient's quality of life and lead to permanent brain damage. Although medical research has identified certain genetic risk factors, the specific pathogenesis of the disorder remains unclear. Despite the prevalence of research employing magnetic resonance imaging, few studies have focused on the gene level and gene expression profile involving a large number of screened genes. However, the high dimensionality of genetic data presents a great challenge to accurately modeling the data. To tackle the current challenges, this study presents a novel feature selection strategy that utilizes heuristic feature fusion and a multi-objective optimization genetic algorithm. The goal is to improve classification performance and identify the key gene subset for schizophrenia diagnostics. Traditional gene screening techniques are inadequate for accurately determining the precise number of key genes associated with schizophrenia. Our innovative approach integrates a filter-based feature selection method to reduce data dimensionality and a multi-objective optimization genetic algorithm for improved classification tasks. By combining the filtering and wrapper methods, our strategy leverages their respective strengths in a deliberate manner, leading to superior classification accuracy and a more efficient selection of relevant genes. This approach has demonstrated significant improvements in classification results across 11 out of 14 relevant datasets. The performance on the remaining three datasets is comparable to the existing methods. Furthermore, visual and enrichment analyses have confirmed the practicality of our proposed method as a promising tool for the early detection of schizophrenia.

Retina as a potential biomarker in schizophrenia spectrum disorders: a systematic review and meta-analysis of optical coherence tomography and electroretinography

INTRODUCTION

Abnormal findings on optical coherence tomography (OCT) and electroretinography (ERG) have been reported in participants with schizophrenia spectrum disorders (SSDs). This study aims to reveal the pooled standard mean difference (SMD) in retinal parameters on OCT and ERG among participants with SSDs and healthy controls and their association with demographic characteristics, clinical symptoms, smoking, diabetes mellitus, and hypertension.

METHODS

Using PubMed, Scopus, Web of Science, and PSYNDEX, we searched the literature from inception to March 31, 2023, using specific search terms. This study was registered with PROSPERO (CRD4202235795) and conducted according to PRISMA 2020.

RESULTS

We included 65 studies in the systematic review and 44 in the meta-analysis. Participants with SSDs showed thinning of the peripapillary retinal nerve fiber layer (pRNFL), macular ganglion cell layer- inner plexiform cell layer, and retinal thickness in all other segments of the macula. A meta-analysis of studies that excluded SSD participants with diabetes and hypertension showed no change in results, except for pRNFL inferior and nasal thickness. Furthermore, a significant difference was found in the pooled SMD of pRNFL temporal thickness between the left and right eyes. Meta-regression analysis revealed an association between retinal thinning and duration of illness, positive and negative symptoms. In OCT angiography, no differences were found in the foveal avascular zone and superficial layer foveal vessel density between SSD participants and controls. In flash ERG, the meta-analysis showed reduced amplitude of both a- and b-waves under photopic and scotopic conditions in SSD participants. Furthermore, the latency of photopic a-wave was significantly shorter in SSD participants in comparison with HCs.

DISCUSSION

Considering the prior report of retinal thinning in unaffected first-degree relatives and the results of the meta-analysis, the findings suggest that retinal changes in SSDs have both trait and state aspects. Future longitudinal multimodal retinal imaging studies are needed to clarify the pathophysiological mechanisms of these changes and to clarify their utility in individual patient monitoring efforts.

Universal method for the isolation of microvessels from frozen brain tissue: A proof-of-concept multiomic investigation of the neurovasculature

The neurovascular unit, comprised of vascular cell types that collectively regulate cerebral blood flow to meet the needs of coupled neurons, is paramount for the proper function of the central nervous system. The neurovascular unit gatekeeps blood-brain barrier properties, which experiences impairment in several central nervous system diseases associated with neuroinflammation and contributes to pathogenesis. To better understand function and dysfunction at the neurovascular unit and how it may confer inflammatory processes within the brain, isolation and characterization of the neurovascular unit is needed. Here, we describe a singular, standardized protocol to enrich and isolate microvessels from archived snap-frozen human and frozen mouse cerebral cortex using mechanical homogenization and centrifugation-separation that preserves the structural integrity and multicellular composition of microvessel fragments. For the first time, microvessels are isolated from postmortem ventromedial prefrontal cortex tissue and are comprehensively investigated as a structural unit using both RNA sequencing and Liquid Chromatography with tandem mass spectrometry (LC-MS/MS). Both the transcriptome and proteome are obtained and compared, demonstrating that the isolated brain microvessel is a robust model for the NVU and can be used to generate highly informative datasets in both physiological and disease contexts.

Microstructural and Microvascular Alterations in Psychotic Spectrum Disorders: A Three-Compartment Intravoxel Incoherent Imaging and Free Water Model

BACKGROUND AND HYPOTHESIS

Microvascular and inflammatory mechanisms have been hypothesized to be involved in the pathophysiology of psychotic spectrum disorders (PSDs). However, data evaluating these hypotheses remain limited.

STUDY DESIGN

We applied a three-compartment intravoxel incoherent motion free water imaging (IVIM-FWI) technique that estimates the perfusion fraction (PF), free water fraction (FW), and anisotropic diffusion of tissue (FAt) to examine microvascular and microstructural changes in gray and white matter in 55 young adults with a PSD compared to 37 healthy controls (HCs).

STUDY RESULTS

We found significantly increased PF, FW, and FAt in gray matter regions, and significantly increased PF, FW, and decreased FAt in white matter regions in the PSD group versus HC. Furthermore, in patients, but not in the HC group, increased PF, FW, and FAt in gray matter and increased PF in white matter were significantly associated with poor performance on several cognitive tests assessing memory and processing speed. We additionally report significant associations between IVIM-FWI metrics and myo-inositol, choline, and N-acetylaspartic acid magnetic resonance spectroscopy imaging metabolites in the posterior cingulate cortex, which further supports the validity of PF, FW, and FAt as microvascular and microstructural biomarkers of PSD. Finally, we found significant relationships between IVIM-FWI metrics and the duration of psychosis in gray and white matter regions.

CONCLUSIONS

The three-compartment IVIM-FWI model provides metrics that are associated with cognitive deficits and may reflect disease progression.

Brain microvascular endothelial cells and blood-brain barrier dysfunction in psychotic disorders

Although there is convergent evidence for blood-brain barrier (BBB) dysfunction and peripheral inflammation in schizophrenia (SZ) and bipolar disorder (BD), it is unknown whether BBB deficits are intrinsic to brain microvascular endothelial cells (BMECs) or arise via effects of peripheral inflammatory cytokines. We examined BMEC function using stem cell-based models to identify cellular and molecular deficits associated with BBB dysfunction in SZ and BD. Induced pluripotent stem cells (iPSCs) from 4 SZ, 4 psychotic BD and 4 healthy control (HC) subjects were differentiated into BMEC-"like" cells. Gene expression and protein levels of tight junction proteins were assessed. Transendothelial electrical resistance (TEER) and permeability were assayed to evaluate BBB function. Cytokine levels were measured from conditioned media. BMECs derived from human iPSCs in SZ and BD did not show differences in BBB integrity or permeability compared to HC BMECs. Outlier analysis using TEER revealed a BBB-deficit (n = 3) and non-deficit (n = 5) group in SZ and BD lines. Stratification based on BBB function in SZ and BD patients identified a BBB-deficit subtype with reduced barrier function, tendency for increased permeability to smaller molecules, and decreased claudin-5 (CLDN5) levels. BMECs from the BBB-deficit group show increased matrix metallopeptidase 1 (MMP1) activity, which correlated with reduced CLDN5 and worse BBB function, and was improved by tumor necrosis factor α (TNFα) and MMP1 inhibition. These results show potential deficits in BMEC-like cells in psychotic disorders that result in BBB disruption and further identify TNFα and MMP1 as promising targets for ameliorating BBB deficits.

Vascular Schizophrenia-like Psychosis in Older Adults

BACKGROUND

The aims of this study were to analyze prevalence and severity of vascular risk factors in older patients referred to our clinic due to onset of Very Late-Onset Schizophrenia-Like Psychosis (VLOSLP) and to create a specific phenotype based on pathophysiological insight rather than age of onset.

METHODS

In a longitudinal study, 103 (M = 39, F = 64; mean age of 80.32 ± 7.65 years) patients were evaluated with cognitive, neuropsychiatric, and functional assessment scales. Blood concentration of hemoglobin (Hb), mean corpuscular volume (MCV), platelets, total protein test (TPT), creatinine, azotemia, glycemia, total cholesterol (TC), triglycerides (TG), uric acid (UA), sodium (Na), potassium (K), chlorine (Cl), calcium (Ca), folate, vitamin B12 (Vit-B12), and homocysteine were measured. Presence/absence of tobacco use, alcohol consumption, psychoactive substance use, hypertension, hyperlipidemia, diabetes mellitus, and history of vascular disease were collected.

RESULTS

Females were more apathetic than males (NPI-Apathy: p = 0.040). Males had a significantly higher level of Hb (p = 0.019) and UA (p = 0.001), and a lower level of platelets (p = 0.004) and Ca (p = 0.003), and used more tobacco (p = 0.046) and alcohol (p = 0.024) than females. Comparing patients < 80 and ≥80 years, we found differences in frequency of vascular risk factors among men (p = 0.027). In total, 102 patients were treated for psychosis (59.16% of them were using atypical antipsychotics).

CONCLUSIONS

The results of this study could be useful for a progressive demonstration of the causal relationship between cardiac and cerebral vascular events and VLOSLP.

Overexpression of transmembrane TNFα in brain endothelial cells induces schizophrenia-relevant behaviors

Upregulation of genes and coexpression networks related to immune function and inflammation have been repeatedly reported in the brain of individuals with schizophrenia. However, a causal relationship between the abnormal immune/inflammation-related gene expression and schizophrenia has not been determined. We conducted co-expression networks using publicly available RNA-seq data from prefrontal cortex (PFC) and hippocampus (HP) of 64 individuals with schizophrenia and 64 unaffected controls from the SMRI tissue collections. We identified proinflammatory cytokine, transmembrane tumor necrosis factor-α (tmTNFα), as a potential regulator in the module of co-expressed genes that we find related to the immune/inflammation response in endothelial cells (ECs) and/or microglia of the brain of individuals with schizophrenia. The immune/inflammation-related modules associated with schizophrenia and the TNF signaling pathway that regulate the network were replicated in an independent cohort of brain samples from 68 individuals with schizophrenia and 135 unaffected controls. To investigate the association between the overexpression of tmTNFα in brain ECs and schizophrenia-like behaviors, we induced short-term overexpression of the uncleavable form of (uc)-tmTNFα in ECs of mouse brain for 7 weeks. We found schizophrenia-relevant behavioral deficits in these mice, including cognitive impairment, abnormal sensorimotor gating, and sensitization to methamphetamine (METH) induced locomotor activity and METH-induced neurotransmitter levels. These uc-tmTNFα effects were mediated by TNF receptor2 (TNFR2) and induced activation of TNFR2 signaling in astrocytes and neurons. A neuronal module including neurotransmitter signaling pathways was down-regulated in the brain of mice by the short-term overexpression of the gene, while an immune/inflammation-related module was up-regulated in the brain of mice after long-term expression of 22 weeks. Our results indicate that tmTNFα may play a direct role in regulating neurotransmitter signaling pathways that contribute to the clinical features of schizophrenia.

Involvement of an Aberrant Vascular System in Neurodevelopmental, Neuropsychiatric, and Neuro-Degenerative Diseases

The vascular system of the prenatal brain is crucial for the development of the central nervous system. Communication between vessels and neural cells is bidirectional, and dysfunctional communication can lead to neurodevelopmental diseases. In the present review, we introduce neurodevelopmental and neuropsychiatric diseases potentially caused by disturbances in the neurovascular system and discuss candidate genes responsible for neurovascular system impairments. In contrast to diseases that can manifest during the developing stage, we have also summarized the disturbances of the neurovascular system in neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. Furthermore, we discussed the role of abnormal vascularization and dysfunctional vessels in the development of neurovascular-related diseases.

Genome-wide landscape of RNA-binding protein (RBP) networks as potential molecular regulators of psychiatric co-morbidities: a computational analysis

Background

Psychiatric disorders are a major burden on global health. These illnesses manifest as co-morbid conditions, further complicating the treatment. There is a limited understanding of the molecular and regulatory basis of psychiatric co-morbidities. The existing research in this regard has largely focused on epigenetic modulators, non-coding RNAs, and transcription factors. RNA-binding proteins (RBPs) functioning as multi-protein complexes are now known to be predominant controllers of multiple gene regulatory processes. However, their involvement in gene expression dysregulation in psychiatric co-morbidities is yet to be understood.

Results

Ten RBPs (QKI, ELAVL2, EIF2S1, SRSF3, IGF2BP2, EIF4B, SNRNP70, FMR1, DAZAP1, and MBNL1) were identified to be associated with psychiatric disorders such as schizophrenia, major depression, and bipolar disorders. Analysis of transcriptomic changes in response to individual depletion of these RBPs showed the potential influence of a large number of RBPs driving differential gene expression, suggesting functional cross-talk giving rise to multi-protein networks. Subsequent transcriptome analysis of post-mortem human brain samples from diseased and control individuals also suggested the involvement of ~ 100 RBPs influencing gene expression changes. These RBPs were found to regulate various processes including transcript splicing, mRNA transport, localization, stability, and translation. They were also found to form an extensive interactive network. Further, hnRNP, SRSF, and PCBP family RBPs, Matrin3, U2AF2, KHDRBS1, PTBP1, and also PABPN1 were found to be the hub proteins of the RBP network.

Conclusions

Extensive RBP networks involving a few hub proteins could result in transcriptome-wide dysregulation of post-transcriptional modifications, potentially driving multiple psychiatric disorders. Understanding the functional involvement of RBP networks in psychiatric disorders would provide insights into the molecular basis of psychiatric co-morbidities.

Infections, Inflammation, and Psychiatric Illness: Review of Postmortem Evidence

While there is an abundance of epidemiological evidence implicating infectious agents in the etiology of severe mental illnesses, postmortem studies have not yet detected an increased incidence of microbial nucleic acid or proteins in the brains of people with mental illness. Nevertheless, abnormally expressed immune and inflammatory markers have consistently been found in the postmortem brain of patients with schizophrenia and mood disorders. Some of these abnormalities may be the result of an infection in utero or early in life that not only impacted the developing immune system but also the developing neurons of the brain. Some of the immune markers that are consistently found to be upregulated in schizophrenia implicate a possible viral infection and the blood brain barrier in the etiology and neuropathology of the disorder.

Profiling cell-type specific gene expression in post-mortem human brain samples through laser capture microdissection

The transcriptome of a cell constitutes an essential piece of cellular identity and contributes to the multifaceted complexity and heterogeneity of cell-types within the mammalian brain. Thus, while a wealth of studies have investigated transcriptomic alterations underlying the pathophysiology of diseases of the brain, their use of bulk-tissue homogenates makes it difficult to tease apart whether observed differences are explained by disease state or cellular composition. Cell-type-specific enrichment strategies are, therefore, crucial in the context of gene expression profiling. Laser capture microdissection (LCM) is one such strategy that allows for the capture of specific cell-types, or regions of interest, under microscopic visualization. In this review, we focus on using LCM for cell-type specific gene expression profiling in post-mortem human brain samples. We begin with a discussion of various LCM systems, followed by a walk-through of each step in the LCM to gene expression profiling workflow and a description of some of the limitations associated with LCM. Throughout the review, we highlight important considerations when using LCM with post-mortem human brain samples. Whenever applicable, commercially available kits that have proven successful in the context of LCM with post-mortem human brain samples are described.

Exploring the intersection of the microbiome and the developing brain: Impacts on schizophrenia risk

Recent findings show that the perinatal maternal and infant microbiomes have profound potential to impact long term health outcomes. Of particular interest are the ways in which the microbiome influences the developing brain during one of its most critical windows. Schizophrenia and psychosis risk are strongly connected to disruptions in perinatal neurodevelopment. In this review we present an overview of critical aspects in development of both the microbiome and brain, discuss their overlap, and consider what role the microbiome plays in schizophrenia risk during the perinatal window. Considering this, we discuss ways in which expecting and new mothers may reduce offspring schizophrenia risk.

Does Neuroinflammation Underlie the Cognitive Changes Observed With Dietary Interventions?

Dietary interventions, such as calorie restriction and ketogenic diet, have been extensively studied in ageing research, including in cognitive decline. Epidemiological studies indicate beneficial effects of certain dietary regimes on mental health, including mood disorders and dementia. However, randomised-controlled trials (the gold-standard of evidence-based medicine) on calorie restriction diets and the ketogenic diet have yet to show clinically convincing effects in neuropsychiatric disorders. This review will examine the quality of studies and evidence base for the ketogenic and calorie restriction diets in common neuropsychiatric conditions, collating findings from preclinical experiments, case reports or small clinical studies, and randomised controlled clinical trials. The major cellular mechanisms that mediate the effects of these dietary interventions on brain health include neuroinflammation, neuroprotection, and neuromodulation. We will discuss the studies that have investigated the roles of these pathways and their interactions. Popularity of the ketogenic and calorie restriction diets has grown both in the public domain and in psychiatry research, allowing for informed review of the efficacy, the limitations, and the side effects of these diets in specific patient populations. In this review we will summarise the clinical evidence for these diets in neuropsychiatry and make suggestions to improve clinical translation of future research studies.

What genes are differentially expressed in individuals with schizophrenia? A systematic review

Schizophrenia is a severe, complex mental disorder characterized by a combination of positive symptoms, negative symptoms, and impaired cognitive function. Schizophrenia is highly heritable (~80%) with multifactorial etiology and complex polygenic genetic architecture. Despite the large number of genetic variants associated with schizophrenia, few causal variants have been established. Gaining insight into the mechanistic influences of these genetic variants may facilitate our ability to apply these findings to prevention and treatment. Though there have been more than 300 studies of gene expression in schizophrenia over the past 15 years, none of the studies have yielded consistent evidence for specific genes that contribute to schizophrenia risk. The aim of this work is to conduct a systematic review and synthesis of case-control studies of genome-wide gene expression in schizophrenia. Comprehensive literature searches were completed in PubMed, EmBase, and Web of Science, and after a systematic review of the studies, data were extracted from those that met the following inclusion criteria: human case-control studies comparing the genome-wide transcriptome of individuals diagnosed with schizophrenia to healthy controls published between January 1, 2000 and June 30, 2020 in the English language. Genes differentially expressed in cases were extracted from these studies, and overlapping genes were compared to previous research findings from the genome-wide association, structural variation, and tissue-expression studies. The transcriptome-wide analysis identified different genes than those previously reported in genome-wide association, exome sequencing, and structural variation studies of schizophrenia. Only one gene, GBP2, was replicated in five studies. Previous work has shown that this gene may play a role in immune function in the etiology of schizophrenia, which in turn could have implications for risk profiling, prevention, and treatment. This review highlights the methodological inconsistencies that impede valid meta-analyses and synthesis across studies. Standardization of the use of covariates, gene nomenclature, and methods for reporting results could enhance our understanding of the potential mechanisms through which genes exert their influence on the etiology of schizophrenia. Although these results are promising, collaborative efforts with harmonization of methodology will facilitate the identification of the role of genes underlying schizophrenia.

Single-nucleus RNA sequencing of midbrain blood-brain barrier cells in schizophrenia reveals subtle transcriptional changes with overall preservation of cellular proportions and phenotypes

The midbrain is an extensively studied brain region in schizophrenia, in view of its reported dopamine pathophysiology and neuroimmune changes associated with this disease. Besides the dopaminergic system, the midbrain contains other cell types that may be involved in schizophrenia pathophysiology. The neurovascular hypothesis of schizophrenia postulates that both the neurovasculature structure and the functioning of the blood-brain barrier (BBB) are compromised in schizophrenia. In the present study, potential alteration in the BBB of patients with schizophrenia was investigated by single-nucleus RNA sequencing of post-mortem midbrain tissue (15 schizophrenia cases and 14 matched controls). We did not identify changes in the relative abundance of the major BBB cell types, nor in the sub-populations, associated with schizophrenia. However, we identified 14 differentially expressed genes in the cells of the BBB in schizophrenia as compared to controls, including genes that have previously been related to schizophrenia, such as FOXP2 and PDE4D. These transcriptional changes were limited to the ependymal cells and pericytes, suggesting that the cells of the BBB are not broadly affected in schizophrenia.

Prediction of Essential Genes in Comparison States Using Machine Learning

Identifying essential genes in comparison states (EGS) is vital to understanding cell differentiation, performing drug discovery, and identifying disease causes. Here, we present a machine learning method termed Prediction of Essential Genes in Comparison States (PreEGS). To capture the alteration of the network in comparison states, PreEGS extracts topological and gene expression features of each gene in a five-dimensional vector. PreEGS also recruits a positive sample expansion method to address the problem of unbalanced positive and negative samples, which is often encountered in practical applications. Different classifiers are applied to the simulated datasets, and the PreEGS based on the random forests model (PreEGSRF) was chosen for optimal performance. PreEGSRF was then compared with six other methods, including three machine learning methods, to predict EGS in a specific state. On real datasets with four gene regulatory networks, PreEGSRF predicted five essential genes related to leukemia and five enriched KEGG pathways. Four of the predicted essential genes and all predicted pathways were consistent with previous studies and highly correlated with leukemia. With high prediction accuracy and generalization ability, PreEGSRF is broadly applicable for the discovery of disease-causing genes, driver genes for cell fate decisions, and complex biomarkers of biological systems.

Transcriptome Analysis of Post-Mortem Brain Tissue Reveals Up-Regulation of the Complement Cascade in a Subgroup of Schizophrenia Patients

Schizophrenia is a genetically complex neuropsychiatric disorder with largely unresolved mechanisms of pathology. Identification of genes and pathways associated with schizophrenia is important for understanding the development, progression and treatment of schizophrenia. In this study, pathways associated with schizophrenia were explored at the level of gene expression. The study included post-mortem brain tissue samples from 68 schizophrenia patients and 44 age and sex-matched control subjects. Whole transcriptome poly-A selected paired-end RNA sequencing was performed on tissue from the prefrontal cortex and orbitofrontal cortex. RNA expression differences were detected between case and control individuals, focusing both on single genes and pathways. The results were validated with RT-qPCR. Significant differential expression between patient and controls groups was found for 71 genes. Gene ontology analysis of differentially expressed genes revealed an up-regulation of multiple genes in immune response among the patients (corrected p-value = 0.004). Several genes in the category belong to the complement system, including C1R, C1S, C7, FCN3, SERPING1, C4A and CFI. The increased complement expression is primarily driven by a subgroup of patients with increased expression of immune/inflammatory response genes, pointing to important differences in disease etiology within the patient group. Weighted gene co-expression network analysis highlighted networks associated with both synaptic transmission and activation of the immune response. Our results demonstrate the importance of immune-related pathways in schizophrenia and provide evidence for elevated expression of the complement cascade as an important pathway in schizophrenia pathology.

Simple methodology to visualize whole-brain microvasculature in three dimensions

Significance: To explore brain architecture and pathology, a consistent and reliable methodology to visualize the three-dimensional cerebral microvasculature is beneficial. Perfusion-based vascular labeling is quick and easily deliverable. However, the quality of vascular labeling can vary with perfusion-based labels due to aggregate formation, leakage, rapid photobleaching, and incomplete perfusion. Aim: We describe a simple, two-day protocol combining perfusion-based labeling with a two-day clearing step that facilitates whole-brain, three-dimensional microvascular imaging and characterization. Approach: The combination of retro-orbital injection of Lectin-Dylight-649 to label the vasculature, the clearing process of a modified iDISCO+ protocol, and light-sheet imaging collectively enables a comprehensive view of the cerebrovasculature. Results: We observed ∼ threefold increase in contrast-to-background ratio of Lectin-Dylight-649 vascular labeling over endogenous green fluorescent protein fluorescence from a transgenic mouse model. With light-sheet microscopy, we demonstrate sharp visualization of cerebral microvasculature throughout the intact mouse brain. Conclusions: Our tissue preparation protocol requires fairly routine processing steps and is compatible with multiple types of optical microscopy.

Brain-immune interactions in neuropsychiatric disorders: Lessons from transcriptome studies for molecular targeting

Understanding the pathophysiological mechanisms of neuropsychiatric disorders has been a challenging quest for neurobiologists. Recent years have witnessed enormous technological advances in the field of neuroimmunology, blurring boundaries between the central nervous system and the periphery. Consequently, the discipline has expanded to cover interactions between the nervous and immune systems in health and diseases. The complex interplay between the peripheral and central immune pathways in neuropsychiatric disorders has recently been documented in various studies, but the genetic determinants remain elusive. Recent transcriptome studies have identified dysregulated genes involved in peripheral immune cell activation, blood-brain barrier integrity, glial cell activation, and synaptic plasticity in major depressive disorder, bipolar disorder, autism spectrum disorder, and schizophrenia. Herein, the key transcriptomic techniques applied in investigating differentially expressed genes and pathways responsible for altered brain-immune interactions in neuropsychiatric disorders are discussed. The application of transcriptomics that can aid in identifying molecular targets in various neuropsychiatric disorders is highlighted.

Roles of inflammation in intrinsic pathophysiology and antipsychotic drug-induced metabolic disturbances of schizophrenia

Schizophrenia is a debilitating psychiatric illness that remains poorly understood. While the bulk of symptomatology has classically been associated with disrupted brain functioning, accumulating evidence demonstrates that schizophrenia is characterized by systemic inflammation and disturbances in metabolism. Indeed, metabolic disease is a major determinant of the high mortality rate associated with schizophrenia. Antipsychotic drugs (APDs) have revolutionized management of psychosis, making it possible to rapidly control psychotic symptoms. This has ultimately reduced relapse rates of psychotic episodes and improved overall quality of life for people with schizophrenia. However, long-term APD use has also been associated with significant metabolic disturbances including weight gain, dysglycemia, and worsening of the underlying cardiometabolic disease intrinsic to schizophrenia. While the mechanisms for these intrinsic and medication-induced metabolic effects remain unclear, inflammation appears to play a key role. Here, we review the evidence for roles of inflammatory mechanisms in the disease features of schizophrenia and how these mechanisms interact with APD treatment. We also discuss the effects of common inflammatory mediators on metabolic disease. Then, we review the evidence of intrinsic and APD-mediated effects on systemic inflammation in schizophrenia. Finally, we speculate about possible treatment strategies. Developing an improved understanding of inflammatory processes in schizophrenia may therefore introduce new, more effective options for treating not only schizophrenia but also primary metabolic disorders.

Retinal nerve fibre layer and peripapillary vascular density by optical coherence tomography angiography in schizophrenia

Clinical relevance: Schizophrenia is a progressive disease. Analysis of retinal nerve fibre layer and peripapillary vascular density by optical coherence tomography angiography in schizophrenia patients may help to explain the pathophysiology of the disease.Background: Both macular and optic nerve microvascular structures can be visualised with optical coherence tomography angiography. Few studies have evaluated retinal vessels in patients with schizophrenia. Some of these studies suggest that larger retinal venules are associated with the severity of psychotic symptoms.Methods: This study evaluated retinal nerve fibre layer thickness and peripapillary vascular density by optical coherence tomography angiography in 22 eyes of 22 patients with schizophrenia and 26 eyes of 26 healthy control subjects. All peripapillary quadrants were evaluated with 4.5 × 4.5 mm images.Results: In the schizophrenia group, retinal nerve fibre layer thickness was significantly thinner and the mean peripapillary vascular density values were significantly lower in the temporal quadrant than in the control group (p < 0.05), but was similar in the peripapillary, superior, inferior, and nasal quadrants (p > 0.05). Peripapillary vascular density values and retinal nerve fibre layer thickness in schizophrenia patients were found to be lower in temporal quadrant compared to healthy eyes.Conclusion: Evaluation of the retina with optical coherence tomography angiography may be useful in detecting and monitoring progressive neurodegeneration in patients with schizophrenia.

Altered levels of immune cell adhesion molecules are associated with memory impairment in schizophrenia and healthy controls

Increased cytokines and increased intercellular adhesion molecule-1 (ICAM1) found in the schizophrenia prefrontal cortex and in the blood may relate to cognitive deficits. Endothelial ICAM1 regulates immune cell trafficking into the brain by binding to integrins located on the surface of leukocytes. Whether the circulating levels of the main ICAM1 adhesion partners, lymphocyte-function associated antigen-1 (LFA1) and complement receptor 3 (CR3), both integrins, are altered in schizophrenia is unknown. Gene expressions of ICAM1, LFA1 and CR3 were measured in leukocytes from 86 schizophrenia patients and 77 controls. Participants were also administered cognitive testing to determine the extent to which cognitive ability was related to molecular measures of leukocyte adhesion. This cohort was previously stratified into inflammatory subgroups based on circulating cytokine mRNAs; thus, gene expressions were analysed by diagnosis and by inflammatory subgroups. Previously measured plasma ICAM1 protein was elevated in "high inflammation" schizophrenia compared to both "high" and "low inflammation" controls while ICAM1 mRNA was unchanged in leukocytes. LFA1 mRNA was decreased and CR3 mRNA was increased in leukocytes from people with schizophrenia compared to controls. LFA1 mRNA levels were positively correlated with working memory and elevated soluble ICAM1 was negatively correlated with verbal memory in schizophrenia. Altogether, some of the cognitive deficits in schizophrenia may be associated with altered expression of molecules that regulate immune cell trafficking.

The Role of Brain Microvascular Endothelial Cell and Blood-Brain Barrier Dysfunction in Schizophrenia

BACKGROUND

Despite decades of research, little clarity exists regarding pathogenic mechanisms related to schizophrenia. Investigations on the disease biology of schizophrenia have primarily focused on neuronal alterations. However, there is substantial evidence pointing to a significant role for the brain's microvasculature in mediating neuroinflammation in schizophrenia.

SUMMARY

Brain microvascular endothelial cells (BMEC) are a central element of the microvasculature that forms the blood-brain barrier (BBB) and shields the brain against toxins and immune cells via paracellular, transcellular, transporter, and extracellular matrix proteins. While evidence for BBB dysfunction exists in brain disorders, including schizophrenia, it is not known if BMEC themselves are functionally compromised and lead to BBB dysfunction.

KEY MESSAGES

Genome-wide association studies, postmortem investigations, and gene expression analyses have provided some insights into the role of the BBB in schizophrenia pathophysiology. However, there is a significant gap in our understanding of the role that BMEC play in BBB dysfunction. Recent advances differentiating human BMEC from induced pluripotent stem cells (iPSC) provide new avenues to examine the role of BMEC in BBB dysfunction in schizophrenia.

Cilia interactome with predicted protein-protein interactions reveals connections to Alzheimer's disease, aging and other neuropsychiatric processes

Cilia are dynamic microtubule-based organelles present on the surface of many eukaryotic cell types and can be motile or non-motile primary cilia. Cilia defects underlie a growing list of human disorders, collectively called ciliopathies, with overlapping phenotypes such as developmental delays and cognitive and memory deficits. Consistent with this, cilia play an important role in brain development, particularly in neurogenesis and neuronal migration. These findings suggest that a deeper systems-level understanding of how ciliary proteins function together may provide new mechanistic insights into the molecular etiologies of nervous system defects. Towards this end, we performed a protein-protein interaction (PPI) network analysis of known intraflagellar transport, BBSome, transition zone, ciliary membrane and motile cilia proteins. Known PPIs of ciliary proteins were assembled from online databases. Novel PPIs were predicted for each ciliary protein using a computational method we developed, called High-precision PPI Prediction (HiPPIP) model. The resulting cilia "interactome" consists of 165 ciliary proteins, 1,011 known PPIs, and 765 novel PPIs. The cilia interactome revealed interconnections between ciliary proteins, and their relation to several pathways related to neuropsychiatric processes, and to drug targets. Approximately 184 genes in the cilia interactome are targeted by 548 currently approved drugs, of which 103 are used to treat various diseases of nervous system origin. Taken together, the cilia interactome presented here provides novel insights into the relationship between ciliary protein dysfunction and neuropsychiatric disorders, for e.g. interconnections of Alzheimer's disease, aging and cilia genes. These results provide the framework for the rational design of new therapeutic agents for treatment of ciliopathies and neuropsychiatric disorders.

Identification of Reproducible BCL11A Alterations in Schizophrenia Through Individual-Level Prediction of Coexpression

Previous studies have provided evidence for an alteration of genetic coexpression in schizophrenia (SCZ). However, such analyses have thus far lacked biological specificity for individual genes, which may be critical for identifying illness-relevant effects. Therefore, we applied machine learning to identify gene-specific coexpression differences at the individual subject level and compared these between individuals with SCZ, bipolar disorder, major depressive disorder (MDD), autism spectrum disorder (ASD), and healthy controls. Utilizing transcriptome-wide gene expression data from 21 independent datasets, comprising a total of 9509 participants, we identified a reproducible decrease of BCL11A coexpression across 4 SCZ datasets that showed diagnostic specificity for SCZ when compared with ASD and MDD. We further demonstrate that individual-level coexpression differences can be combined in multivariate coexpression scores that show reproducible illness classification across independent datasets in SCZ and ASD. This study demonstrates that machine learning can capture gene-specific coexpression differences at the individual subject level for SCZ and identify novel biomarker candidates.

Integrating genome-wide association study and methylation functional annotation data identified candidate genes and pathways for schizophrenia

BACKGROUND

Schizophrenia (SCZ) is a severe mental disorder. Both environmental and genetic factors contribute to the development of SCZ. The estimated heritability of SCZ is about 80%. Previous genetic studies of SCZ mainly focused on the genetic variations associated the risk of SCZ. Limited efforts are paid to explore the roles and biological mechanism of nuclear acid methylation implicated in the pathogenesis of SCZ.

METHODS

A two-stage integrative analysis of SCZ GWAS and nuclear acid methylation functional annotation data (including meQTLs and m6A) was performed in this study. First, the discovery GWAS of SCZ was aligned with genomic meQTLs and m6A annotation data to identify the candidate genes associated with SCZ. Second, another independent replication GWAS dataset of SCZ was applied to validate the discovery results. Furthermore, the functional relevance of identified candidate genes with SCZ were validated by the mRNA expression profiling of SCZ brain tissues. Gene ontology (GO) and pathway enrichment analysis of identified candidate genes was performed by the DAVID tool.

RESULTS

The two-stage integrative analysis detected 106 meQTLs related candidate genes for SCZ. After comparing with the differentially expressed genes in SCZ brain tissues, 49 overlapped genes were identified for meQTLs, such as ZSCAN12, BTN3A2 and HLA-DQA1. Besides, for meQTLs, 29 SCZ associated pathways and 56 SCZ associated GO terms were detected, such as cell adhesion molecules and asthma. For m6A, 25 candidate genes were detected by the two-stage integrative analysis for SCZ, such as ZSCAN12, HLA-DQA1 and SNX19. Furthermore, 17 of the 25 genes were detected in the mRNA expression profiling of SCZ brain tissues.

CONCLUSION

This study identified multiple SCZ associated genes and pathways, supporting the implication of nuclear acid methylation in the pathogenesis of SCZ.

Increased macrophages and changed brain endothelial cell gene expression in the frontal cortex of people with schizophrenia displaying inflammation

Elevated pro-inflammatory cytokines exist in both blood and brain of people with schizophrenia but how this affects molecular indices of the blood-brain barrier (BBB) is unclear. Eight mRNAs relating to BBB function, a microglia and three immune cell markers were measured by qPCR in the prefrontal cortex from 37 people with schizophrenia/schizoaffective disorder and 37 matched controls. This cohort was previously grouped into "high inflammation" and "low inflammation" subgroups based on cortical inflammatory-related transcripts. Soluble intercellular adhesion molecule-1 (sICAM1) was measured in the plasma of 78 patients with schizophrenia/schizoaffective disorder and 73 healthy controls. We found that sICAM1 was significantly elevated in schizophrenia. An efflux transporter, ABCG2, was lower, while mRNAs encoding VE-cadherin and ICAM1 were higher in schizophrenia brain. The "high inflammation" schizophrenia subgroup had lower ABCG2 and higher ICAM1, VE-cadherin, occludin and interferon-induced transmembrane protein mRNAs compared to both "low inflammation" schizophrenia and "low inflammation" control subgroups. ICAM1 immunohistochemistry showed enrichment in brain endothelium regardless of diagnosis and was localised to astrocytes in some brains. Microglia mRNA was not altered in schizophrenia nor did it correlate with ICAM1 expression. Immune cell mRNAs were elevated in "high inflammation" schizophrenia compared to both "low inflammation" schizophrenia and controls. CD163+ perivascular macrophages were identified by immunohistochemistry in brain parenchyma in over 40% of "high inflammation" schizophrenia brains. People with high levels of cytokine expression and schizophrenia display changes consistent with greater immune cell transmigration into brain via increased ICAM1, which could contribute to other neuropathological changes found in this subgroup of people.

Age-Associated mRNA and miRNA Expression Changes in the Blood-Brain Barrier

Functional and structural age-associated changes in the blood-brain barrier (BBB) may affect the neurovascular unit and contribute to the onset and progression of age-associated neurodegenerative pathologies, including Alzheimer’s disease. The current study interrogated the RNA profile of the BBB in an ageing human autopsy brain cohort and an ageing mouse model using combined laser capture microdissection and expression profiling. Only 12 overlapping genes were altered in the same direction in the BBB of both ageing human and mouse cohorts. These included genes with roles in regulating vascular tone, tight junction protein expression and cell adhesion, all processes prone to dysregulation with advancing age. Integrated mRNA and miRNA network and pathway enrichment analysis of the datasets identified 15 overlapping miRNAs that showed altered expression. In addition to targeting genes related to DNA binding and/or autophagy, many of the miRNAs identified play a role in age-relevant processes, including BBB dysfunction and regulating the neuroinflammatory response. Future studies have the potential to develop targeted therapeutic approaches against these candidates to prevent vascular dysfunction in the ageing brain.

Cell Type-Specific Laser Capture Microdissection for Gene Expression Profiling in the Human Brain

Cell type-specific laser microdissection technologies in combination with molecular techniques to determine gene expression profiles have become powerful tools to gain insight into the neurobiological basis of neural circuit disturbances in various neurologic or psychiatric diseases. To identify specific cell populations in human postmortem brain tissue, one can use the inherent properties of the cells, such as pigmentation and morphology or their structural composition through immunohistochemistry (IHC). Here, we describe the isolation of homogeneous neurons and oligodendrocytes and the extraction of high-quality RNA from these cells in human postmortem brain using a combination of rapid IHC, Nissl staining, or simple morphology with Laser Capture Microdissection (LCM), or Laser Microdissection (LMD).

Comparative Evaluation of Machine Learning Strategies for Analyzing Big Data in Psychiatry

The requirement of innovative big data analytics has become a critical success factor for research in biological psychiatry. Integrative analyses across distributed data resources are considered essential for untangling the biological complexity of mental illnesses. However, little is known about algorithm properties for such integrative machine learning. Here, we performed a comparative analysis of eight machine learning algorithms for identification of reproducible biological fingerprints across data sources, using five transcriptome-wide expression datasets of schizophrenia patients and controls as a use case. We found that multi-task learning (MTL) with network structure (MTL_NET) showed superior accuracy compared to other MTL formulations as well as single task learning, and tied performance with support vector machines (SVM). Compared to SVM, MTL_NET showed significant benefits regarding the variability of accuracy estimates, as well as its robustness to cross-dataset and sampling variability. These results support the utility of this algorithm as a flexible tool for integrative machine learning in psychiatry.

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.

Blood-brain barrier regulation in psychiatric disorders

The blood-brain barrier (BBB) is a dynamic interface between the peripheral blood supply and the cerebral parenchyma, controlling the transport of material to and from the brain. Tight junctions between the endothelial cells of the cerebral microvasculature limit the passage of large, negatively charged molecules via paracellular diffusion whereas transcellular transportation across the endothelial cell is controlled by a number of mechanisms including transporter proteins, endocytosis, and diffusion. Here, we review the evidence that perturbation of these processes may underlie the development of psychiatric disorders including schizophrenia, autism spectrum disorder (ASD), and affective disorders. Increased permeability of the BBB appears to be a common factor in these disorders, leading to increased infiltration of peripheral material into the brain culminating in neuroinflammation and oxidative stress. However, although there is no common mechanism underpinning BBB dysfunction even within each particular disorder, the tight junction protein claudin-5 may be a clinically relevant target given that both clinical and pre-clinical research has linked it to schizophrenia, ASD, and depression. Additionally, we discuss the clinical significance of the BBB in diagnosis (genetic markers, dynamic contrast-enhanced-magnetic resonance imaging, and blood biomarkers) and in treatment (drug delivery).

Dose-dependent expression of claudin-5 is a modifying factor in schizophrenia

Schizophrenia is a neurodevelopmental disorder that affects up to 1% of the general population. Various genes show associations with schizophrenia and a very weak nominal association with the tight junction protein, claudin-5, has previously been identified. Claudin-5 is expressed in endothelial cells forming part of the blood-brain barrier (BBB). Furthermore, schizophrenia occurs in 30% of individuals with 22q11 deletion syndrome (22q11DS), a population who are haploinsufficient for the claudin-5 gene. Here, we show that a variant in the claudin-5 gene is weakly associated with schizophrenia in 22q11DS, leading to 75% less claudin-5 being expressed in endothelial cells. We also show that targeted adeno-associated virus-mediated suppression of claudin-5 in the mouse brain results in localized BBB disruption and behavioural changes. Using an inducible 'knockdown' mouse model, we further link claudin-5 suppression with psychosis through a distinct behavioural phenotype showing impairments in learning and memory, anxiety-like behaviour and sensorimotor gating. In addition, these animals develop seizures and die after 3-4 weeks of claudin-5 suppression, reinforcing the crucial role of claudin-5 in normal neurological function. Finally, we show that anti-psychotic medications dose-dependently increase claudin-5 expression in vitro and in vivo while aberrant, discontinuous expression of claudin-5 in the brains of schizophrenic patients post mortem was observed compared to age-matched controls. Together, these data suggest that BBB disruption may be a modifying factor in the development of schizophrenia and that drugs directly targeting the BBB may offer new therapeutic opportunities for treating this disorder.

Laser microdissection and gene expression profiling in the human postmortem brain

Laser microdissection in combination with gene expression profiling using postmortem human brain tissue provides a powerful approach to interrogating cell type-specific pathologies within neural circuits that are known to be dysfunctional in neuropsychiatric disorders. The success of these experiments critically depends on a number of factors, such as the cellular purity of the sample, the quality of the RNA, the methodologies of data normalization and computational data analysis, and how data are interpreted. Data obtained from these experiments should be validated at the protein level. Furthermore, from the perspective of disease mechanism discovery, it would be ideal to investigate whether manipulation of the expression of genes identified as differentially expressed can rescue or ameliorate the neurobiologic or behavioral phenotypes associated with the specific disease. Thus, the ultimate value of this approach rests upon the fact that the generation of novel disease-related pathophysiologic hypotheses may lead to deeper understanding of disease mechanisms and possible development of effective targeted treatments.

The blood-brain barrier in psychosis

Blood-brain barrier pathology is recognised as a central factor in the development of many neurological disorders, but much less is known about the role of the blood-brain barrier in psychiatric disorders. We review post-mortem, serum-biomarker, CSF-biomarker, and neuroimaging studies that have examined blood-brain barrier structure and function in schizophrenia and related psychoses. We consider how blood-brain barrier dysfunction could relate to glutamatergic and inflammatory abnormalities, which are increasingly understood to play a part in the pathogenesis of psychosis. Mechanisms by which the blood-brain barrier and its associated solute transporters moderate CNS availability of antipsychotic drugs are summarised. We conclude that the complex nature of blood-brain barrier dysfunction in psychosis might be relevant to many aspects of disrupted neuronal and synaptic function, increased permeability to inflammatory molecules, disrupted glutamate homoeostasis, impaired action of antipsychotics, and development of antipsychotic resistance. Future research should address the longitudinal course of blood-brain barrier alterations in psychosis, to determine whether blood-brain barrier dysfunction is a cause or consequence of the pathology associated with the disorder.

Microvascular anomaly conditions in psychiatric disease. Schizophrenia - angiogenesis connection

Schizophrenia (SZ) is a severe mental disorder with unknown etiology and elusive neuropathological and neurobiological features have been a focus of many theoretical hypotheses and empirical studies. Current genetic and neurobiology information relevant to SZ implicates neuronal developmental and synaptic plasticity abnormalities, and neurotransmitter, microglial and oligodendrocytes dysfunction. Several recent theories have highlighted the neurovascular unit as a potential contributor to the pathophysiology of SZ. We explored the biological plausibility of a link between SZ and the neurovascular system by examining insights gained from genetic, neuroimaging and postmortem studies, which include gene expression and neuropathology analyses. We also reviewed information from animal models of cerebral angiogenesis in order to understand better the complex interplay between angiogenic and neurotrophic factors in development, vascular endothelium/blood brain barrier remodeling and maintenance, all of which contribute to sustaining adequate regional blood flow and safeguarding normal brain function. Microvascular and hemodynamic alterations in SZ highlight the importance of further research and reveal the neurovascular unit as a potential therapeutic target in SZ.

Microvascular anomaly conditions in psychiatric disease. Schizophrenia - angiogenesis connection

Schizophrenia (SZ) is a severe mental disorder with unknown etiology and elusive neuropathological and neurobiological features have been a focus of many theoretical hypotheses and empirical studies. Current genetic and neurobiology information relevant to SZ implicates neuronal developmental and synaptic plasticity abnormalities, and neurotransmitter, microglial and oligodendrocytes dysfunction. Several recent theories have highlighted the neurovascular unit as a potential contributor to the pathophysiology of SZ. We explored the biological plausibility of a link between SZ and the neurovascular system by examining insights gained from genetic, neuroimaging and postmortem studies, which include gene expression and neuropathology analyses. We also reviewed information from animal models of cerebral angiogenesis in order to understand better the complex interplay between angiogenic and neurotrophic factors in development, vascular endothelium/blood brain barrier remodeling and maintenance, all of which contribute to sustaining adequate regional blood flow and safeguarding normal brain function. Microvascular and hemodynamic alterations in SZ highlight the importance of further research and reveal the neurovascular unit as a potential therapeutic target in SZ.

Abnormal Grey Matter Arteriolar Cerebral Blood Volume in Schizophrenia Measured With 3D Inflow-Based Vascular-Space-Occupancy MRI at 7T

Metabolic dysfunction and microvascular abnormality may contribute to the pathogenesis of schizophrenia. Most previous studies of cerebral perfusion in schizophrenia measured total cerebral blood volume (CBV) and cerebral blood flow (CBF) in the brain, which reflect the ensemble signal from the arteriolar, capillary, and venular compartments of the microvasculature. As the arterioles are the most actively regulated blood vessels among these compartments, they may be the most sensitive component of the microvasculature to metabolic disturbances. In this study, we adopted the inflow-based vascular-space-occupancy (iVASO) MRI approach to investigate alterations in the volume of small arterial (pial) and arteriolar vessels (arteriolar cerebral blood volume [CBVa]) in the brain of schizophrenia patients. The iVASO approach was extended to 3-dimensional (3D) whole brain coverage, and CBVa was measured in the brains of 12 schizophrenia patients and 12 matched controls at ultra-high magnetic field (7T). Significant reduction in grey matter (GM) CBVa was found in multiple areas across the whole brain in patients (relative changes of 14%-51% and effect sizes of 0.7-2.3). GM CBVa values in several regions in the temporal cortex showed significant negative correlations with disease duration in patients. GM CBVa increase was also found in a few brain regions. Our results imply that microvascular abnormality may play a role in schizophrenia, and suggest GM CBVa as a potential marker for the disease. Further investigation is needed to elucidate whether such effects are due to primary vascular impairment or secondary to other causes, such as metabolic dysfunction.

Generating testable hypotheses for schizophrenia and rheumatoid arthritis pathogenesis by integrating epidemiological, genomic, and protein interaction data

Patients with schizophrenia and their relatives have reduced prevalence of rheumatoid arthritis. Schizophrenia and rheumatoid arthritis genome-wide association studies also indicate negative genetic correlations, suggesting that there may be shared pathogenesis at the DNA level or downstream. A portion of the inverse prevalence could be attributed to pleiotropy, i.e., variants of a single nucleotide polymorphism that could confer differential risk for these disorders. To study the basis for such an interrelationship, we initially compared lists of single nucleotide polymorphisms with significant genetic associations (p < 1e-8) for schizophrenia or rheumatoid arthritis, evaluating patterns of linkage disequilibrium and apparent pleiotropic risk profiles. Single nucleotide polymorphisms that conferred risk for both schizophrenia and rheumatoid arthritis were localized solely to the extended HLA region. Among single nucleotide polymorphisms that conferred differential risk for schizophrenia and rheumatoid arthritis, the majority were localized to HLA-B, TNXB, NOTCH4, HLA-C, HCP5, MICB, PSORS1C1, and C6orf10; published functional data indicate that HLA-B and HLA-C have the most plausible pathogenic roles in both disorders. Interactomes of these eight genes were constructed from protein-protein interaction information using publicly available databases and novel computational predictions. The genes harboring apparently pleiotropic single nucleotide polymorphisms are closely connected to rheumatoid arthritis and schizophrenia associated genes through common interacting partners. A separate and independent analysis of the interactomes of rheumatoid arthritis and schizophrenia genes showed a significant overlap between the two interactomes and that they share several common pathways, motivating functional studies suggesting a relationship in the pathogenesis of schizophrenia/rheumatoid arthritis.

Neurovascular Unit Dysfunction and Blood-Brain Barrier Hyperpermeability Contribute to Schizophrenia Neurobiology: A Theoretical Integration of Clinical and Experimental Evidence

Schizophrenia is a psychotic disorder characterized by delusions, hallucinations, negative symptoms, as well as behavioral and cognitive dysfunction. It is a pathoetiologically heterogeneous disorder involving complex interrelated mechanisms that include oxidative stress and neuroinflammation. Neurovascular endothelial dysfunction and blood-brain barrier (BBB) hyperpermeability are established mechanisms in neurological disorders with comorbid psychiatric symptoms such as epilepsy, traumatic brain injury, and Alzheimer's disease. Schizophrenia is frequently comorbid with medical conditions associated with peripheral vascular endothelial dysfunction, such as metabolic syndrome, cardiovascular disease, and diabetes mellitus. However, the existence and etiological relevance of neurovascular endothelial dysfunction and BBB hyperpermeability in schizophrenia are still not well recognized. Here, we review the growing clinical and experimental evidence, indicating that neurovascular endotheliopathy and BBB hyperpermeability occur in schizophrenia patients. We present a theoretical integration of human and animal data linking oxidative stress and neuroinflammation to neurovascular endotheliopathy and BBB breakdown in schizophrenia. These abnormalities may contribute to the cognitive and behavioral symptoms of schizophrenia via several mechanisms involving reduced cerebral perfusion and impaired homeostatic processes of cerebral microenvironment. Furthermore, BBB disruption can facilitate interactions between brain innate and peripheral adaptive immunity, thereby perpetuating harmful neuroimmune signals and toxic neuroinflammatory responses, which can also contribute to the symptoms of schizophrenia. Taken together, these findings support the "mild encephalitis" hypothesis of schizophrenia. If neurovascular abnormalities prove to be etiologically relevant to the neurobiology of schizophrenia, then targeting these abnormalities may represent a promising therapeutic strategy.

Morphometric analysis of the cerebral expression of ATP-binding cassette transporter protein ABCB1 in chronic schizophrenia: Circumscribed deficits in the habenula

There is increasing evidence that microvascular abnormalities and malfunction of the blood-brain barrier (BBB) significantly contribute to schizophrenia pathophysiology. The ATP-binding cassette transporter ABCB1 is an important molecular component of the intact BBB, which has been implicated in a number of neurodegenerative and psychiatric disorders, including schizophrenia. However, the regional and cellular expression of ABCB1 in schizophrenia is yet unexplored. Therefore, we studied ABCB1 protein expression immunohistochemically in twelve human post-mortem brain regions known to play a role in schizophrenia, in 13 patients with schizophrenia and nine controls. In ten out of twelve brain regions under study, no significant differences were found with regard to the numerical density of ABCB1-expressing capillaries between all patients with schizophrenia and control cases. The left and right habenular complex, however, showed significantly reduced capillary densities in schizophrenia patients. In addition, we found a significantly reduced density of ABCB1-expressing neurons in the left habenula. Reduced ABCB1 expression in habenular capillaries might contribute to increased brain levels of proinflammatory cytokines in patients with schizophrenia, while decreased expression of this protein in a subpopulation of medial habenular neurons (which are probably purinergic) might be related to abnormalities of purines and their receptors found in this disease.

A combined analysis of genome-wide expression profiling of bipolar disorder in human prefrontal cortex

Numbers of gene expression profiling studies of bipolar disorder have been published. Besides different array chips and tissues, variety of the data processes in different cohorts aggravated the inconsistency of results of these genome-wide gene expression profiling studies. By searching the gene expression databases, we obtained six data sets for prefrontal cortex (PFC) of bipolar disorder with raw data and combinable platforms. We used standardized pre-processing and quality control procedures to analyze each data set separately and then combined them into a large gene expression matrix with 101 bipolar disorder subjects and 106 controls. A standard linear mixed-effects model was used to calculate the differentially expressed genes (DEGs). Multiple levels of sensitivity analyses and cross validation with genetic data were conducted. Functional and network analyses were carried out on basis of the DEGs. In the result, we identified 198 unique differentially expressed genes in the PFC of bipolar disorder and control. Among them, 115 DEGs were robust to at least three leave-one-out tests or different pre-processing methods; 51 DEGs were validated with genetic association signals. Pathway enrichment analysis showed these DEGs were related with regulation of neurological system, cell death and apoptosis, and several basic binding processes. Protein-protein interaction network further identified one key hub gene. We have contributed the most comprehensive integrated analysis of bipolar disorder expression profiling studies in PFC to date. The DEGs, especially those with multiple validations, may denote a common signature of bipolar disorder and contribute to the pathogenesis of disease.

Neuropil pruning in Early-Course Schizophrenia: Immunological, Clinical, and Neurocognitive Correlates

INTRODUCTION

Neuropathological studies suggest neuropil reduction in schizophrenia. Altered synaptic pruning is proposed to underlie neuropil reduction. Underlying factors and clinical correlates of synaptic pruning are poorly understood. Using phosphorus magnetic resonance spectroscopy (31P MRS), it is feasible to assess membrane phospholipid (MPL) metabolites in the brain that specifically and sensitively reflect neuropil expansion (elevated MPL precursors) or contraction (elevated MPL catabolites).

METHODS

We examined MPL metabolites and their cognitive, clinical and immunologic correlates among 28 early-course schizophrenia individuals (illness duration 1.99±1.33 years; antipsychotic-naïve=18) and 21 controls. We acquired whole-brain multi-voxel 31P MRS data from 12 unique brain regions. Interleukin-6 and C-reactive protein (CRP) were assayed in the serum. Generalized linear mixed models examined case-control differences in MPL metabolites in these regions correcting for multiple testing. Partial correlations accounting for multiple tests examined the relationship of Interleukin-6 and CRP levels with MPL metabolite levels.

RESULTS

MPL catabolite levels were increased in the thalamus in schizophrenia compared to controls. Interleukin-6 and CRP levels did not show case-control differences. Interleukin-6 levels positively correlated with MPL catabolite levels in the thalamus after correcting for multiple tests. The left thalamus MPL catabolite levels correlated negatively with sustained attention (corrected p=0.039).

DISCUSSION

Elevated MPL catabolites in the thalamus suggest increased neuropil contraction that may be related to excessive synaptic pruning. The thalamic neuropil contraction is associated with Interleukin-6 levels suggesting central pathogenic mechanisms for the inflammatory mediators. Correlation of increased thalamic MPL catabolite levels with cognitive impairments suggests clinical correlates of neuropil contraction.

Transcriptome sequencing of the choroid plexus in schizophrenia

The choroid plexus (CP) has a key role in maintaining brain homeostasis by producing cerebrospinal fluid (CSF), by mediating transport of nutrients and removing metabolic products from the central nervous system and by responding to peripheral inflammatory signals. Although abnormal markers of immune response and inflammation are apparent in individuals with schizophrenia, the CP of these individuals has not been characterized. We therefore sequenced mRNA from the CP from two independent collections of individuals with schizophrenia and unaffected controls. Genes related to immune function and inflammation were upregulated in both collections. In addition, a co-expression module related to immune/inflammation response that was generated by combining mRNA-Seq data from both collections was significantly associated with disease status. The immune/inflammation-related co-expression module was positively correlated with levels of C-reactive protein (CRP), cortisol and several immune modulator proteins in the serum of the same individuals and was also positively correlated with CRP, cortisol and pro-inflammatory cytokines in the frontal cortex of the same individuals. In addition, we found a substantial number of nodes (genes) that were common to our schizophrenia-associated immune/inflammation module from the pooled data and a module we generated from lippopolysaccharides-treated mouse model data. These results suggest that the CP of individuals with schizophrenia are responding to signals from the periphery by upregulating immune/inflammation-related genes to protect the brain and maintain the homeostasis but nevertheless fails to completely prevent immune/inflammation related changes in the brain.

Protein Interaction Networks Link Schizophrenia Risk Loci to Synaptic Function

Schizophrenia is a severe and highly heritable psychiatric disorder affecting approximately 1% of the population. Genome-wide association studies have identified 108 independent genetic loci with genome-wide significance but their functional importance has yet to be elucidated. Here, we develop a novel strategy based on network analysis of protein-protein interactions (PPI) to infer biological function associated with variants most strongly linked to illness risk. We show that the schizophrenia loci are strongly linked to synaptic transmission (P _FWE < .001) and ion transmembrane transport (P _FWE = .03), but not to ontological categories previously found to be shared across psychiatric illnesses. We demonstrate that brain expression of risk-linked genes within the identified processes is strongly modulated during birth and identify a set of synaptic genes consistently changed across multiple brain regions of adult schizophrenia patients. These results suggest synaptic function as a developmentally determined schizophrenia process supported by the illness's most associated genetic variants and their PPI networks. The implicated genes may be valuable targets for mechanistic experiments and future drug development approaches.

Somatic Comorbidity in Schizophrenia: Some Possible Biological Mechanisms Across the Life Span

Schizophrenia is associated with decreased life expectancy (15-25 y) compared to the general population, with comorbid somatic diseases and in particular cardiovascular diseases being a major cause. Life style and medication probably account for much of the increased mortality risk due to somatic diseases in schizophrenia, but the evidence implicating biological pathways potentially affecting both body and brain is increasing. This includes overlapping genes between schizophrenia and somatic diseases, prenatal risk factors such as hypoxia and infections, and increased cardiovascular disease risk in drug-naïve patients at illness onset. Although environmental bias increases throughout the disease course, there are also some studies on chronic schizophrenia and postmortem brain samples that warrant further attention. In the following, we will attempt to move beyond environmental impact and explore some of the shared pathophysiological mechanisms potentially underlying both schizophrenia and somatic diseases.

Differential expression of transcriptional regulatory units in the prefrontal cortex of patients with bipolar disorder: potential role of early growth response gene 3

Bipolar disorder (BD) is a severe mental illness with a strong genetic component. Despite its high degree of heritability, current genetic studies have failed to reveal individual loci of large effect size. In lieu of focusing on individual genes, we investigated regulatory units (regulons) in BD to identify candidate transcription factors (TFs) that regulate large groups of differentially expressed genes. Network-based approaches should elucidate the molecular pathways governing the pathophysiology of BD and reveal targets for potential therapeutic intervention. The data from a large-scale microarray study was used to reconstruct the transcriptional associations in the human prefrontal cortex, and results from two independent microarray data sets to obtain BD gene signatures. The regulatory network was derived by mapping the significant interactions between known TFs and all potential targets. Five regulons were identified in both transcriptional network models: early growth response 3 (EGR3), TSC22 domain family, member 4 (TSC22D4), interleukin enhancer-binding factor 2 (ILF2), Y-box binding protein 1 (YBX1) and MAP-kinase-activating death domain (MADD). With a high stringency threshold, the consensus across tests was achieved only for the EGR3 regulon. We identified EGR3 in the prefrontal cortex as a potential key target, robustly repressed in both BD signatures. Considering that EGR3 translates environmental stimuli into long-term changes in the brain, disruption in biological pathways involving EGR3 may induce an impaired response to stress and influence on risk for psychiatric disorders, particularly BD.

Evidence of microvascular dysfunction in patients with cystic fibrosis

Cystic fibrosis (CF) is a genetic, multisystemic disorder with broad clinical manifestations apart from the well-characterized pulmonary dysfunction. Recent findings have described impairment in conduit vessel function in patients with CF; however, whether microvascular function is affected in this population has yet to be elucidated. Using laser-Doppler imaging, we evaluated microvascular function through postocclusive reactive hyperemia (PORH), local thermal hyperemia (LTH), and iontophoresis with acetylcholine (ACh). PORH [518 ± 174% (CF) and 801 ± 125% (control), P = 0.039], LTH [1,338 ± 436% (CF) and 1,574 ± 620% (control), P = 0.045], and iontophoresis with ACh [416 ± 140% (CF) and 617 ± 143% (control), P = 0.032] were significantly lower in patients with CF than control subjects. In addition, the ratio of PORH to LTH was significantly (P = 0.043) lower in patients with CF (55.3 ± 5.1%) than control subjects (68.8 ± 3.1%). Significant positive correlations between LTH and forced expiratory volume in 1 s (%predicted) (r = 0.441, P = 0.013) and between the PORH-to-LTH ratio and exercise capacity (r = 0.350, P = 0.049) were observed. These data provide evidence of microvascular dysfunction in patients with CF compared with control subjects. In addition, our data demonstrate a complex relationship between microvascular function and classical markers of disease severity (i.e., pulmonary function and exercise capacity) in CF.

An integrative genome-wide transcriptome reveals that candesartan is neuroprotective and a candidate therapeutic for Alzheimer's disease

BACKGROUND

Alzheimer's disease is the most frequent age-related dementia, and is currently without treatment. To identify possible targets for early therapeutic intervention we focused on glutamate excitotoxicity, a major early pathogenic factor, and the effects of candesartan, an angiotensin receptor blocker of neuroprotective efficacy in cell cultures and rodent models of Alzheimer's disease. The overall goal of the study was to determine whether gene analysis of drug effects in a primary neuronal culture correlate with alterations in gene expression in Alzheimer's disease, thus providing further preclinical evidence of beneficial therapeutic effects.

METHODS

Primary neuronal cultures were treated with candesartan at neuroprotective concentrations followed by excitotoxic glutamate amounts. We performed genome-wide expression profile analysis and data evaluation by ingenuity pathway analysis and gene set enrichment analysis, compared with alterations in gene expression from two independent published datasets identified by microarray analysis of postmortem hippocampus from Alzheimer's disease patients. Preferential expression in cerebrovascular endothelial cells or neurons was analyzed by comparison to published gene expression in these cells isolated from human cortex by laser capture microdissection.

RESULTS

Candesartan prevented glutamate upregulation or downregulation of several hundred genes in our cultures. Ingenuity pathway analysis and gene set enrichment analysis revealed that inflammation, cardiovascular disease and diabetes signal transduction pathways and amyloid β metabolism were major components of the neuronal response to glutamate excitotoxicity. Further analysis showed associations of glutamate-induced changes in the expression of several hundred genes, normalized by candesartan, with similar alterations observed in hippocampus from Alzheimer's disease patients. Gene analysis of neurons and cerebrovascular endothelial cells obtained by laser capture microdissection revealed that genes up- and downregulated by glutamate were preferentially expressed in endothelial cells and neurons, respectively.

CONCLUSIONS

Our data may be interpreted as evidence of direct candesartan neuroprotection beyond its effects on blood pressure, revealing common and novel disease mechanisms that may underlie the in vitro gene alterations reported here and glutamate-induced cell injury in Alzheimer's disease. Our observations provide novel evidence for candesartan neuroprotection through early molecular mechanisms of injury in Alzheimer's disease, supporting testing this compound in controlled clinical studies in the early stages of the illness.

Drosophila Shep and C. elegans SUP-26 are RNA-binding proteins that play diverse roles in nervous system development

The Caenorhabditis elegans gene sup-26 encodes a well-conserved RNA-recognition motif-containing RNA-binding protein (RBP) that functions in dendrite morphogenesis of the PVD sensory neuron. The Drosophila ortholog of sup-26, alan shepard (shep), is expressed throughout the nervous system and has been shown to regulate neuronal remodeling during metamorphosis. Here, we extend these studies to show that sup-26 and shep are required for the development of diverse cell types within the nematode and fly nervous systems during embryonic and larval stages. We ascribe roles for sup-26 in regulating dendrite number and the expression of genes involved in mechanosensation within the nematode peripheral nervous system. We also find that in Drosophila, shep regulates dendrite length and branch order of nociceptive neurons, regulates the organization of neuronal clusters of the peripheral nervous system and the organization of axons within the ventral nerve cord. Taken together, our results suggest that shep/sup-26 orthologs play diverse roles in neural development across animal species. Moreover, we discuss potential roles for shep/sup-26 orthologs in the human nervous system.