Comprehensive evaluation of positional candidates in the IL-18 pathway reveals suggestive associations with schizophrenia and herpes virus seropositivity

Association between cognitive function and IL-18 levels in schizophrenia: Dependent on IL18 - 607 A/C polymorphism

Accumulating evidence suggests that immune system dysregulation is associated with debilitating neurodevelopment in schizophrenia (SZ). Cognitive impairment is a persistent feature that occurs during the onset of SZ and persists throughout the course of the disease. Early studies have found that elevated interleukin (IL)- 18 interacts with IL18 polymorphism and is correlated with psychotic symptoms in SZ. This study aimed to investigate whether elevated IL-18 levels interacted with the -607 A/C polymorphism to determine cognitive decline in patients with chronic SZ. We recruited 693 inpatients and 422 healthy controls to measure IL-18 levels and genotype the - 607 A/C polymorphism. Further, cognitive function was measured by the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). We found that IL-18 serum levels were higher in patients than those in healthy controls, and were not associated with IL18 - 607 A/C in combined subjects or either patients or healthy controls, respectively. Moreover, - 607 A/C was correlated with the visuospatial/constructional index only in the patients. In addition, our research found that IL-18 levels were positively correlated to immediate memory only in patients with the C/C genotype, but not in patients with C/A or A/A genotype. This study suggests that the relationship of IL-18 with cognitive function depends on the IL18 - 607 A/C polymorphism of SZ patients.

Gene-Environment Interactions in Schizophrenia: A Literature Review

Schizophrenia is a devastating mental illness with a strong genetic component that is the subject of extensive research. Despite the high heritability, it is well recognized that non-genetic factors such as certain infections, cannabis use, psychosocial stress, childhood adversity, urban environment, and immigrant status also play a role. Whenever genetic and non-genetic factors co-exist, interaction between the two is likely. This means that certain exposures would only be of consequence given a specific genetic makeup. Here, we provide a brief review of studies reporting evidence of such interactions, exploring genes and variants that moderate the effect of the environment to increase risk of developing psychosis. Discovering these interactions is crucial to our understanding of the pathogenesis of complex disorders. It can help in identifying individuals at high risk, in developing individualized treatments and prevention plans, and can influence clinical management.

Elevated levels of IL-18 associated with schizophrenia and first episode psychosis: A systematic review and meta-analysis

AIM

To determine whether interleukin 18 (IL-18) is elevated in the blood of schizophrenia (SCZ) and first episode psychosis patients, as well as investigate whether this potential relationship is causal.

METHOD

We conducted a systematic review and meta-analysis of IL-18 levels in the blood of SCZ patients, comprising of both chronic and first episode psychosis (FEP) cohorts. To investigate causality, we undertook the two-sample Mendelian randomization (MR) study.

RESULTS

A total of eight studies were included in our meta-analysis, our results did indeed show an association between elevated levels of IL-18 and SCZ compared to healthy controls (Z = 3.50, P = .0005). This association remained significant in subsequent subgroup analyses for chronic (Z = 3.15, P = .002) and achieved borderline significance in FEP (Z = 1.93, P = .05) SCZ. Our MR analysis failed to detect any causal relationship between IL-18 levels and SCZ.

CONCLUSION

The results of our study demonstrate that even though IL-18 levels are elevated in SCZ patients, IL-18 levels do not seem to cause of the disorder itself. Our findings suggest that IL-18 may have utility as a biomarker of SCZ and aid in research into the early intervention of the disease.

Cytokine Imbalance in Schizophrenia. From Research to Clinic: Potential Implications for Treatment

Cytokines are one of the most important components of the immune system. They orchestrate the brain's response to infectious and other exogenous insults and are crucial mediators of the cross-talk between the nervous and immune systems. Epidemiological studies have demonstrated that severe infections and autoimmune disorders, in addition to genetic predisposition, are risk factors for schizophrenia. Furthermore, maternal infection during pregnancy appears to increase the risk of schizophrenia, and proinflammatory cytokines may be negatively involved in the neurodevelopmental process. A cytokine imbalance has been described in the blood and cerebrospinal fluid of schizophrenia patients, particularly in the T helper type 1 [Th1] and type 2 [Th2] cytokines, albeit the results of such studies appear to be contradictory. Chronic stress, likewise, appears to contribute to a lasting proinflammatory state and likely also promotes the disorder. The aim of this mini-review is to investigate the roles of different cytokines in the pathophysiology of schizophrenia and define how cytokines may represent key molecular targets to regulate for the prevention and treatment of schizophrenia. How current antipsychotic drugs impact cytokine networks is also evaluated. In this context, we propose to change the focus of schizophrenia from a traditionally defined brain disorder, to one that is substantially impacted by the periphery and immune system.

Rps27a might act as a controller of microglia activation in triggering neurodegenerative diseases

Neurodegenerative diseases (NDDs) are increasing serious menaces to human health in the recent years. Despite exhibiting different clinical phenotypes and selective neuronal loss, there are certain common features in these disorders, suggesting the presence of commonly dysregulated pathways. Identifying causal genes and dysregulated pathways can be helpful in providing effective treatment in these diseases. Interestingly, in spite of the considerable researches on NDDs, to the best of our knowledge, no dysregulated genes and/or pathways were reported in common across all the major NDDs so far. In this study, for the first time, we have applied the three-way interaction model, as an approach to unravel sophisticated gene interactions, to trace switch genes and significant pathways that are involved in six major NDDs. Subsequently, a gene regulatory network was constructed to investigate the regulatory communication of statistically significant triplets. Finally, KEGG pathway enrichment analysis was applied to find possible common pathways. Because of the central role of neuroinflammation and immune system responses in both pathogenic and protective mechanisms in the NDDs, we focused on immune genes in this study. Our results suggest that "cytokine-cytokine receptor interaction" pathway is enriched in all of the studied NDDs, while "osteoclast differentiation" and "natural killer cell mediated cytotoxicity" pathways are enriched in five of the NDDs each. The results of this study indicate that three pathways that include "osteoclast differentiation", "natural killer cell mediated cytotoxicity" and "cytokine-cytokine receptor interaction" are common in five, five and six NDDs, respectively. Additionally, our analysis showed that Rps27a as a switch gene, together with the gene pair {Il-18, Cx3cl1} form a statistically significant and biologically relevant triplet in the major NDDs. More specifically, we suggested that Cx3cl1 might act as a potential upstream regulator of Il-18 in microglia activation, and in turn, might be controlled with Rps27a in triggering NDDs.

Increased interleukin 18 activity in adolescents with early-onset psychosis is associated with cortisol and depressive symptoms

OBJECTIVE

Evidence indicates that the pathophysiology of adult psychosis involves immune dysregulation, but its associations with stress are often not considered. The inflammatory cytokine interleukin (IL)-18, which is elevated in adult schizophrenia, is suggested to be sensitive to stress. We compared the associations of IL-18 with cortisol and clinical variables in adolescents with early-onset psychosis (EOP) aged 12-18 years and age-matched healthy controls (HC).

METHOD

We measured serum IL-18, IL-18 binding protein (IL-18BP), IL-18 receptor accessory protein (IL-18RAP), IL-18 receptor 1 (IL-18R1) and cortisol, and calculated the IL-18/IL-18BP ratio in patients (n = 31) and HC (n = 60). Psychotic symptoms were assessed using the Positive and Negative Syndrome Scale and depressive symptoms by the Mood and Feelings Questionnaire-Child version (MFQ-C). Bivariate correlation analysis was used to explore relationships between IL-18/IL-18BP ratio and cortisol, depression and other clinical characteristics. Hierarchical multiple linear regression analysis was used to assess their individual contributions to the variance of the IL-18/IL-18BP ratio.

RESULTS

Patients had significantly higher IL-18 levels and IL-18/IL-18BP ratios than HC, but similar IL-18BP, IL-18RAP and IL-18R1. Both cortisol (R² change = 0.05) and the MFQ-C score (R² change = 0.09) contributed significantly to the variance in IL-18/IL-18BP ratios after controlling for confounders.

CONCLUSION

We found increased IL-18 system activity in adolescents with EOP. Cortisol and depressive symptoms each contributed to the variance in the IL-18/IL-18BP ratio. Our findings support activation of inflammatory pathways in adolescent psychosis and suggest interactions between stress, inflammation and depressive symptoms in EOP.

Cannabinoid CB2 Receptor Gene and Environmental Interaction in the Development of Psychiatric Disorders

CB2 cannabinoid receptor (CB2R) gene is associated with depression. We investigated the gene-environment interaction between CB2R function and diverse stressors. First, anxiety-like behavior during chronic-mild-stress (CMS) was evaluated in C57BL/6JJmsSlc mice following treatment with CB2R agonist JWH015 or inverse-agonist AM630. Second, locomotor activity and anxiety-like behavior were measured following exposure to an immune poly I:C stressor. Gene expressions of HPA axis related molecules, Fkbp5, Nr3c1 and Crf and pro-inflammatory cytokine Il-1b, as well as Bdnf as a key neurotrophin that supports neuron health, function, and synaptic plasticity, were determined in hippocampus of Cnr2 knockout mice, as indicators of stressful environment. CMS-induced anxiety-like behavior was enhanced by AM630 and reduced by JWH015 and fluvoxamine. Poly I:C reduced locomotor activity and increased anxiety-like behavior, and these effects were pronounced in the heterozygote than in the wild type mice. Fkbp5 and Nr3c1 expression were lower in the Cnr2 heterozygotes than in the wild type mice with Poly I:C treatment. These findings indicate that interaction between CB2R gene and stressors increases the risk of depression-like behaviors that may be linked with neuro-immune crosstalk. Further studies in human subjects are necessary to determine the role of CB2R and environmental interaction in the development of depression.

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.

Epigenetics in Schizophrenia: A Pilot Study of Global DNA Methylation in Different Brain Regions Associated with Higher Cognitive Functions

Attempts to discover genes that are involved in the pathogenesis of major psychiatric disorders have been frustrating and often fruitless. Concern is building about the need to understand the complex ways in which nature and nurture interact to produce mental illness. We analyze the epigenome in several brain regions from schizophrenic patients with severe cognitive impairment using high-resolution (450K) DNA methylation array. We identified 139 differentially methylated CpG sites included in known and novel candidate genes sequences as well as in and intergenic sequences which functions remain unknown. We found that altered DNA methylation is not restricted to a particular region, but includes others such as CpG shelves and gene bodies, indicating the presence of different DNA methylation signatures depending on the brain area analyzed. Our findings suggest that epimutations are not relatables between different tissues or even between tissues' regions, highlighting the need to adequately study brain samples to obtain reliable data concerning the epigenetics of schizophrenia.

Neuroimmune biomarkers in schizophrenia

Schizophrenia is a heterogeneous psychiatric disorder with a broad spectrum of clinical and biological manifestations. Due to the lack of objective tests, the accurate diagnosis and selection of effective treatments for schizophrenia remains challenging. Numerous technologies have been employed in search of schizophrenia biomarkers. These studies have suggested that neuroinflammatory processes may play a role in schizophrenia pathogenesis, at least in a subgroup of patients. The evidence indicates alterations in both pro- and anti-inflammatory molecules in the central nervous system, which have also been found in peripheral tissues and may correlate with schizophrenia symptoms. In line with these findings, certain immunomodulatory interventions have shown beneficial effects on psychotic symptoms in schizophrenia patients, in particular those with distinct immune signatures. In this review, we evaluate these findings and their potential for more targeted drug interventions and the development of companion diagnostics. Although currently no validated markers exist for schizophrenia patient stratification or the prediction of treatment efficacy, we propose that utilisation of inflammatory markers for diagnostic and theranostic purposes may lead to novel therapeutic approaches and deliver more effective care for schizophrenia patients.

Serum IL-18 level, clinical symptoms and IL-18-607A/C polymorphism among chronic patients with schizophrenia in a Chinese Han population

Literature suggests that alterations in the inflammatory and immune systems are involved in the pathogenesis of schizophrenia. Specifically, patients diagnosed with schizophrenia exhibit increased IL-18, a pleiotropic proinflammatory cytokine in type 1 T-helper (Th1) responses. The functional 607A/C promoter polymorphism of the IL-18 gene is also associated with the psychopathology of this disorder. However, no current study has explored its role in the clinical symptoms of schizophrenia as mediated through IL-18 levels. We recruited 772 inpatients with schizophrenia and 775 healthy controls in a Han Chinese population and genotyped the IL-18-607A/C polymorphism. Patient psychopathology was assessed using the Positive and Negative Syndrome Scale (PANSS). Serum IL-18 levels were measured in 80 patients and 93 healthy controls. Our results showed that there were no significant differences in the distribution of the allele and genotype frequencies between the patients and controls. Both increased IL-18 serum level and the IL-18-607A/C polymorphism were positively associated with the PANSS general psychopathology subscore and the PANSS total score. Moreover, interaction of increased IL-18 serum level and the IL-18-607A/C polymorphism influenced the clinical psychopathological symptoms, indicating that association of IL-18 level with the PANSS general psychopathology subscale or the total scores was present only among patients carrying the C allele. We demonstrate an association between the IL-18-607A/C variant and clinical psychopathological symptoms in schizophrenia. Findings suggest that the association between higher IL-18 levels and clinical symptoms in schizophrenia is dependent on the IL-18-607A/C polymorphism.

Altered interleukin-18 levels are associated with cognitive impairment in chronic schizophrenia

The pathophysiology of cognitive deficits in schizophrenia may involve the neuroinflammation mediated by cytokines. This study examined the IL-18 levels, the cognitive function, and their association in schizophrenia. We recruited 70 chronic patients and 75 normal controls and examined the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and IL-18 levels. Positive and Negative Syndrome Scale (PANSS) was assessed in chronic patients. IL-18 levels were increased in chronic patients as compared to normal controls (p < 0.01). RBANS total score and the subscales of immediate memory and delayed memory were lower in patients than controls (all p < 0.001). In patients, IL-18 levels were positively associated with RBANS total score and the subscales of immediate and delayed memory (all p < 0.05). Multiple regression analysis further confirmed that IL-18 was an independent contributor to RBANS total score and the aforementioned two indexes (all p < 0.05). Our data demonstrate that immune responses may play an important role in cognitive deficits in schizophrenia and the abnormal levels of IL-18 reflecting the disturbed balance of proinflammatory and anti-inflammatory mechanisms may be relevant to cognitive deficits of this disorder.

Potential involvement of the interleukin-18 pathway in schizophrenia

OBJECTIVE

Accumulating evidence implicates inflammatory cytokines in the development of psychiatric disorders, including schizophrenia (SZ). IL-18 is one of cytokines that plays a crucial role in immune response and neurodevelopment. We aimed to investigate potential genetic alterations of the cytokine system underpinning SZ.

METHODS

We tested the association of genetic variants within the cytokine-cytokine receptor interaction (CCRI) pathway with SZ, using GWAS-derived data involving 768 adult SZ patients and 1348 controls, and replicated the association of IL18R1 rs1035130 with SZ in an independent sample of 1957 adult patients and 1509 controls. We compared expression levels of IL18, IL18R1 and IL18RAP in peripheral blood of a cohort of adolescent participants (<18 years), including 14 early-onset SZ patients and 13 healthy controls. Furthermore, we carried out a cis-eQTL (expression Quantitative Trait Loci) and a cis-mQTL (Methylation Quantitative Trait Loci) analysis for IL18R1 rs1035130.

RESULTS

In the discovery stage, we detected association signals within two IL18 pathway genes, IL18R1 and IL18RAP, with the most significant marker being IL18R1 rs1035130 (P = 1.84E-7, OR = 0.70). In the validation stage, we found rs1035130 was associated with SZ (P = 0.028, OR = 0.89). Expressions of IL18 and IL18R1 were altered in blood of SZ patients compared with 13 controls. Furthermore, cis-QTL analyses indicated that rs1035130 was associated with an eQTL and 5 mQTLs.

CONCLUSION

Our findings suggest the alteration of IL18 pathway may contribute to the psychopathology of SZ.

Animal models of gene-environment interaction in schizophrenia: A dimensional perspective

Schizophrenia has long been considered as a disorder with multifactorial origins. Recent discoveries have advanced our understanding of the genetic architecture of the disease. However, even with the increase of identified risk variants, heritability estimates suggest an important contribution of non-genetic factors. Various environmental risk factors have been proposed to play a role in the etiopathogenesis of schizophrenia. These include season of birth, maternal infections, obstetric complications, adverse events at early childhood, and drug abuse. Despite the progress in identification of genetic and environmental risk factors, we still have a limited understanding of the mechanisms whereby gene-environment interactions (G × E) operate in schizophrenia and psychoses at large. In this review we provide a critical analysis of current animal models of G × E relevant to psychotic disorders and propose that dimensional perspective will advance our understanding of the complex mechanisms of these disorders.

Interleukin 18 and cognitive impairment in first episode and drug naïve schizophrenia versus healthy controls

Alterations in the inflammatory and immune systems have been documented to occur from the earliest stages of schizophrenia, and have been associated with neurodevelopmental changes. Cognitive impairment is a core feature in the pathology of schizophrenia, and recent studies showed a significant increase in serum IL-18 in schizophrenia, and a putative role of IL-18 in neuroprogression and thus neurocognitive defects. The purpose of this study was to examine the association of IL-18 with cognitive deficits in schizophrenia. We recruited 77 first episode and drug naïve schizophrenic patients and 75 healthy control subjects and examined the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and serum IL-18 in both groups. Schizophrenic symptoms were assessed using the positive and negative syndrome scale (PANSS). We found that IL-18 levels were non-significantly higher in patients than controls (206.0±92.9 pg/ml vs 193.2±41.8 pg/ml, p=0.28). Cognitive scores on the RBANS and nearly all of its five subscales (all p<0.05) except for the Visuospatial/Constructional index (p>0.05) were significantly lower in schizophrenic patients than normal controls. For the patients, IL-18 was positively associated with the Visuospatial/Constructional domain of cognitive deficits in schizophrenia. Our findings suggest that cognitive deficits occur during the acute stage of a schizophrenic episode, and IL-18 may be involved in Visuospatial/Constructional deficits of these patients.

Genetic variation in IL18R1 and IL18 genes and Inteferon γ ELISPOT response to smallpox vaccination: an unexpected relationship

BACKGROUND

Genetic association studies demonstrated a role for cytokine proteins and cytokine or cytokine receptor gene polymorphisms in smallpox vaccine-induced adaptive immunity.

METHODS

We examined the association of genetic polymorphisms with cellular (interferon [IFN] γ enzyme-linked immunospot assay [ELISPOT]) immune response to smallpox vaccine in 1076 immunized individuals.

RESULTS

The majority of significant associations were discovered between single-nucleotide polymorphisms/haplotypes in IL18R1 and IL18 genes, in which we previously reported an association with vaccinia virus-induced neutralizing antibody titers in this study cohort. A functional coding IL18R1 polymorphism (rs1035130/Phe251Phe; P = .01) was significantly associated with an allele dose-related increase in IFN-γ production and was also associated with vaccinia-specific neutralizing antibody titers. Significant associations were also found between IL18R1 haplotypes and variations in IFN-γ ELISPOT responses (global P < .0001).

CONCLUSIONS

Our data suggest the importance of variants in the IL18R1 and IL18 genetic loci for broad-based smallpox vaccine-induced adaptive immunity.

Missing and Possible Link between Neuroendocrine Factors, Neuropsychiatric Disorders, and Microglia

Endocrine systems have long been suggested to be one of the important factors in neuropsychiatric disorders, while the underlying mechanisms have not been well understood. Traditionally, neuropsychiatric disorders have been mainly considered the consequence of abnormal conditions in neural circuitry. Beyond the neuronal doctrine, microglia, one of the glial cells with inflammatory/immunological functions in the central nervous system (CNS), have recently been suggested to play important roles in neuropsychiatric disorders. However, the crosstalk between neuroendocrine factors, neuropsychiatric disorders, and microglia has been unsolved. Therefore, we herein introduce and discuss a missing and possible link between these three factors; especially highlighting the following hormones; (1) Hypothalamic-Pituitary-Adrenal (HPA) axis-related hormones such as corticotropin-releasing hormone (CRH) and glucocorticoids, (2) sex-related hormones such as estrogen and progesterone, and (3) oxytocin. A growing body of evidence has suggested that these hormones have a direct effect on microglia. We hypothesize that hormone-induced microglial activation and the following microglia-derived mediators may lead to maladaptive neuronal networks including synaptic dysfunctions, causing neuropsychiatric disorders. Future investigations to clarify the correlation between neuroendocrine factors and microglia may contribute to a novel understanding of the pathophysiology of neuropsychiatric disorders.

Elevated levels of circulating IL-18BP and perturbed regulation of IL-18 in schizophrenia

Background

The pleiotropic pro-inflammatory cytokine Interleukin (IL)-18 has been proposed to play a role in schizophrenia, since elevated circulating levels of its protein and altered frequencies of genetic variants in its molecular system are reported in schizophrenic patients.

Methods

We analyzed 77 patients with schizophrenia diagnosis (SCZ) and 77 healthy control subjects (HC) for serum concentration of both IL-18 and its natural inhibitor, the IL-18 binding protein (IL-18BP).

Results

We confirmed that serum levels of total IL-18 are significantly increased in SCZ, as compared to HC. However, due to a highly significant increase in levels of circulating IL-18BP in SCZ, as compared to HC, the levels of free, bioactive IL-18 are not significantly different between the two groups. In addition, the relationships between the levels of IL-18 and its inhibitor, as well as between the two molecules and age appear dissimilar for SCZ and HC. In particular, the elevated levels of IL-18BP, likely a consequence of the body’s attempt to counteract the early prominent inflammation which characterizes schizophrenia, are maintained in earlier and later stages of the disease. However, the IL-18BP elevation appears ineffective to balance the IL-18 system in younger SCZ patients, while in older patients the levels of circulating bioactive IL-18 are comparable to those of HC, if not lower.

Conclusions

In conclusion, these findings indicate that the IL-18 system is perturbed in schizophrenia, supporting the idea that this pro-inflammatory cytokine might be part of a pathway of genetic and environmental components for vulnerability to the disease.

Elevated interleukin-18 serum levels in chronic schizophrenia: Association with psychopathology

BACKGROUND

Schizophrenia is associated with various abnormalities in the immune system including elevated levels of Interleukin-18 (IL-18), a potent inflammatory cytokine in T-helper 1 (Th1) responses. The aim of this study was to assess the clinical significance of serum IL-18 levels in various stages of schizophrenia.

METHODS

We measured serum IL-18 levels using a sandwich enzyme-linked immunosorbent assay (ELISA) from 78 never-medicated first-episode schizophrenia, 79 medicated chronic schizophrenia and 78 healthy control subjects. The symptoms of schizophrenia were assessed by the Positive and Negative Syndrome Scale (PANSS).

RESULTS

The chronic patients had significantly greater serum IL-18 levels than both first-episode patients and controls. Serum IL-18 was also positively correlated with the PANSS general psychopathology subscore in chronic schizophrenic patients.

CONCLUSIONS

Our results showed elevated IL-18 pathway activity may be involved in the psychopathology of schizophrenia.

Recent advances in psychoneuroimmunology: Inflammation in psychiatric disorders

Psychiatric disorders are common and complex and their precise biological underpinnings remain elusive. Multiple epidemiological, molecular, genetic and gene expression studies suggest that immune system dysfunction may contribute to the risk for developing psychiatric disorders including schizophrenia, bipolar disorder, and major depressive disorder. However, the precise mechanisms by which inflammation-related events confer such risk are unclear. In this review, we examine the peripheral and central evidence for inflammation in psychiatric disorders and the potential molecular mechanisms implicated including inhibition of neurogenesis, apoptosis, the HPA-axis, the role of brain-derived neurotrophic factor and the interplay between the glutamatergic, dopaminergic and serotonergic neurotransmitter systems.

Identification of blood biomarkers for psychosis using convergent functional genomics

There are to date no objective clinical laboratory blood tests for psychotic disease states. We provide proof of principle for a convergent functional genomics (CFG) approach to help identify and prioritize blood biomarkers for two key psychotic symptoms, one sensory (hallucinations) and one cognitive (delusions). We used gene expression profiling in whole blood samples from patients with schizophrenia and related disorders, with phenotypic information collected at the time of blood draw, then cross-matched the data with other human and animal model lines of evidence. Topping our list of candidate blood biomarkers for hallucinations, we have four genes decreased in expression in high hallucinations states (Fn1, Rhobtb3, Aldh1l1, Mpp3), and three genes increased in high hallucinations states (Arhgef9, Phlda1, S100a6). All of these genes have prior evidence of differential expression in schizophrenia patients. At the top of our list of candidate blood biomarkers for delusions, we have 15 genes decreased in expression in high delusions states (such as Drd2, Apoe, Scamp1, Fn1, Idh1, Aldh1l1), and 16 genes increased in high delusions states (such as Nrg1, Egr1, Pvalb, Dctn1, Nmt1, Tob2). Twenty-five of these genes have prior evidence of differential expression in schizophrenia patients. Predictive scores, based on panels of top candidate biomarkers, show good sensitivity and negative predictive value for detecting high psychosis states in the original cohort as well as in three additional cohorts. These results have implications for the development of objective laboratory tests to measure illness severity and response to treatment in devastating disorders such as schizophrenia.

Neonatal infection with neurotropic influenza A virus induces the kynurenine pathway in early life and disrupts sensorimotor gating in adult Tap1-/- mice

Epidemiological studies suggest that early life infections may contribute to the development of neuropsychiatric disorders later in life. Experimental studies employing infections during neonatal life support this notion by reporting persistent changes in the behaviour of adult animals, including deficits in sensorimotor gating. We have previously described an induction of the kynurenine pathway in neonatal wild-type (WT) mice following a systemic infection with neurotropic influenza A/WSN/33 virus. Here, we use the same model of infection in both WT and Tap1-/- mice (expressing reduced levels of MHC class I) and study long-term effects of the infection on sensorimotor gating, as determined by measuring prepulse inhibition (PPI). Moreover, transcription of genes encoding enzymes in the kynurenine pathway and levels of kynurenic acid (KYNA), in the brain of Tap1-/- mice were investigated. In mice infected on postnatal day (P)3 or P4, the levels of several transcripts in the kynurenine pathway were altered at P7, P13 and P24. Transcripts encoding indoleamine-pyrrole 2,3-dioxygenase (IDO), degrading tryptophan in the first step of the kynurenine pathway were consistently up-regulated at all time-points investigated. The changes in transcript levels were accompanied by a transient elevation of KYNA in the brain of infected mice at P13. At age 5-6 months, neonatally infected Tap1-/-, but not WT, mice exhibited a reduction in PPI. The present data show that a neonatal infection targeting the brain can induce the kynurenine pathway and that such an infection can disrupt sensorimotor gating in adulthood in genetically vulnerable mice.

Grey matter changes associated with host genetic variation and exposure to Herpes Simplex Virus 1 (HSV1) in first episode schizophrenia

BACKGROUND

We previously reported reduced prefrontal cortex (PFC) grey matter volume among first episode, antipsychotic-naïve schizophrenia subjects (SZ) exposed to HSV1 but not among healthy subjects (HS) (Prasad et al., 2007). Independently, rs1051788, an exonic polymorphism of the MHC Class I polypeptide-related sequence B (MICB) gene was associated with HSV1 seropositivity, as well as SZ risk. In this study, we examined whether PFC grey matter changes associated with HSV1 exposure varied against the background of MICB genotypes.

METHODS

We examined Caucasian individuals from the sample we studied in our previous report (Prasad et al., 2007) (SZ, n=21 and HS, n=19). Whole brain voxelwise analysis of structural MRI scans was conducted using Statistical Parametric Mapping, ver 5 (SPM5). The impact of rs1051788 variation and HSV1 seropositivity on grey matter volumes was examined using regression models on the combined sample of cases and controls, and then within each diagnostic group.

RESULTS

In the combined sample of cases and controls, we observed the main effects of HSV1 seropositivity and genotypes, and a significant joint effect of HSV1 seropositivity and genotype mainly in the PFC. The joint effect was more prominent among cases than among controls.

DISCUSSION

Our observations suggest that rs1051788 and HSV1 seropositivity are associated individually and jointly with reduced PFC grey matter volume. The patterns of these associations differ by diagnostic status, and these factors explain only a "small" portion of the variance in the grey matter volume reductions.

Schizophrenia susceptibility genes directly implicated in the life cycles of pathogens: cytomegalovirus, influenza, herpes simplex, rubella, and Toxoplasma gondii

Many genes implicated in schizophrenia can be related to glutamatergic transmission and neuroplasticity, oligodendrocyte function, and other families clearly related to neurobiology and schizophrenia phenotypes. Others appear rather to be involved in the life cycles of the pathogens implicated in the disease. For example, aspartylglucosaminidase (AGA), PLA2, SIAT8B, GALNT7, or B3GAT1 metabolize chemical ligands to which the influenza virus, herpes simplex, cytomegalovirus (CMV), rubella, or Toxoplasma gondii bind. The epidermal growth factor receptor (EGR/EGFR) is used by the CMV to gain entry to cells, and a CMV gene codes for an interleukin (IL-10) mimic that binds the host cognate receptor, IL10R. The fibroblast growth factor receptor (FGFR1) is used by herpes simplex. KPNA3 and RANBP5 control the nuclear import of the influenza virus. Disrupted in schizophrenia 1 (DISC1) controls the microtubule network that is used by viruses as a route to the nucleus, while DTNBP1, MUTED, and BLOC1S3 regulate endosomal to lysosomal routing that is also important in viral traffic. Neuregulin 1 activates ERBB receptors releasing a factor, EBP1, known to inhibit the influenza virus transcriptase. Other viral or bacterial components bind to genes or proteins encoded by CALR, FEZ1, FYN, HSPA1B, IL2, HTR2A, KPNA3, MED12, MED15, MICB, NQO2, PAX6, PIK3C3, RANBP5, or TP53, while the cerebral infectivity of the herpes simplex virus is modified by Apolipoprotein E (APOE). Genes encoding for proteins related to the innate immune response, including cytokine related (CCR5, CSF2RA, CSF2RB, IL1B, IL1RN, IL2, IL3, IL3RA, IL4, IL10, IL10RA, IL18RAP, lymphotoxin-alpha, tumor necrosis factor alpha [TNF]), human leukocyte antigen (HLA) antigens (HLA-A10, HLA-B, HLA-DRB1), and genes involved in antigen processing (angiotensin-converting enzyme and tripeptidyl peptidase 2) are all concerned with defense against invading pathogens. Human microRNAs (Hsa-mir-198 and Hsa-mir-206) are predicted to bind to influenza, rubella, or poliovirus genes. Certain genes associated with schizophrenia, including those also concerned with neurophysiology, are intimately related to the life cycles of the pathogens implicated in the disease. Several genes may affect pathogen virulence, while the pathogens in turn may affect genes and processes relevant to the neurophysiology of schizophrenia. For such genes, the strength of association in genetic studies is likely to be conditioned by the presence of the pathogen, which varies in different populations at different times, a factor that may explain the heterogeneity that plagues such studies. This scenario also suggests that drugs or vaccines designed to eliminate the pathogens that so clearly interact with schizophrenia susceptibility genes could have a dramatic effect on the incidence of the disease.

Neonatal infection with neurotropic influenza A virus affects working memory and expression of type III Nrg1 in adult mice

Epidemiological studies suggest that early life infections may contribute to the development of psychiatric disorders characterized by cognitive deficits. Here, we studied the effects of a neonatal influenza A/WSN/33 virus infection on locomotor activity, working memory and emotional behavior in adult mice. In addition to wild type mice, immunodeficient (Tap1(-/-)) mice lacking functional CD8(+) T cells, were included in the study to model the potential influence of a genetic deficit relating to virus clearance. Three to four months after the infection, infected Tap1(-/-) mice, but not wild type mice, exhibited deficits in working memory as well as increased rearing activity and anxiety. In the medial prefrontal cortices of these infected Tap1(-/-) mice reduced levels of type III Nrg1 transcripts were observed supporting a role for neuregulin 1 signaling in neuronal circuits involved in working memory. Virus replication, distribution or clearance did not differ between the two genotypes. The lack of CD8(+) T cells, however, appeared to contribute to a more pronounced glia response in Tap1(-/-) than in wild type mice. Thus, the present study suggest that the risk of developing deficits in cognitive and emotional behavior following a CNS infection during brain development is influenced by genetic variation in genes involved in the immune response.

Mapping of the full length and the truncated interleukin-18 receptor alpha in the mouse brain

The cytokine IL-18 acts on the CNS both in physiological and pathological conditions. Its action occurs through the heterodimeric receptor IL-18Ralpha\beta. To better understand IL-18 central effects, we investigated in the mouse brain the distribution of two IL-18Ralpha transcripts, a full length and an isoform lacking the intracellular domain hypothesized to be a decoy receptor. Both isoforms were expressed in neurons throughout the brain primarily with overlapping distribution but also with some unique pattern. These data suggest that IL-18 may modulate neuronal functions and that its action may be regulated through expression of a decoy receptor.

Lack of association between polymorphisms of the IL18R1 and IL18RAP genes and cardiovascular risk: the MORGAM Project

Background

Interleukin-18 is a pro-inflammatory cytokine suspected to be associated with atherosclerosis and its complications. We had previously shown that one single nucleotide polymorphism (SNP) of the IL18 gene was associated with cardiovascular disease (CVD) through an interaction with smoking. As a further step for elucidating the contribution of the IL-18 pathway to the etiology of CVD, we here investigated the association between the genetic variability of two IL-18 receptor genes, IL18R1 and IL18RAP, with the risk of developing CVD.

Methods

Eleven tagging SNPs, 5 in IL18R1 and 6 in IL18RAP, characterizing the haplotypic variability of the corresponding genes; were genotyped in 5 European prospective CVD cohorts including 1416 cases and 1772 non-cases, as part of the MORGAM project. Both single-locus and haplotypes analyses were carried out to investigate the association of these SNPs with CVD.

Results

We did not find any significant differences in allele, genotype and haplotype frequencies between cases and non-cases for either of the two genes. Moreover, the search for interactions between SNPs located in different genes, including 5 IL18 SNPs previously studied in the MORGAM project, and between SNPs and environmental factors remained unfruitful.

Conclusion

Our analysis suggests that the variability of IL18R1 and IL18RAP genes are unlikely to contribute to modulate the risk of CVD.

Antibodies to cytomegalovirus and Herpes Simplex Virus 1 associated with cognitive function in schizophrenia

BACKGROUND

Cognitive impairment in the form of decreased working memory and executive functions has been recognized as a key deficit in schizophrenia. Neurotropic viruses have been associated with focal gray matter deficits in patients with schizophrenia. We evaluated whether such agents alter cognitive function in schizophrenia.

METHODS

The sample consisted of 329 patients diagnosed with schizophrenia or schizoaffective disorder. We evaluated associations between exposure to selected agents (Herpes Simplex Viruses 1 and 2 (HSV1, HSV2 respectively) cytomegalovirus (CMV) and Toxoplasma gondii) and scores on the Trail Making Test (TMT), controlling for relevant variables.

RESULTS

Serological evidence of exposure to CMV was associated with impaired performance on TMT part A time to completion (p=0.044), a measure of visual search, working memory, and psychomotor speed. Both CMV and HSV1 were significantly associated with increased errors on TMT part B (p<0.001 for both viruses). HSV2 and T. gondii exposure measures were not associated with any of the cognitive functions evaluated using TMT.

CONCLUSIONS

Both CMV and HSV1 are associated with impaired cognitive function in schizophrenia as measured by the TMT. Further analyses to evaluate the impact of other illness related variables including genetic variants are warranted.