Interleukin-1 gene complex in schizophrenia: an association study

Neuroinflammation in schizophrenia: the role of nuclear factor kappa B

Neuroinflammation, particularly in the dorsolateral prefrontal cortex, is well-established in a subset of people with schizophrenia, with significant increases in inflammatory markers including several cytokines. Yet the cause(s) of cortical inflammation in schizophrenia remains unknown. Clues as to potential microenvironmental triggers and/or intracellular deficits in immunoregulation may be gleaned from looking further upstream of effector immune molecules to transcription factors that control inflammatory gene expression. Here, we focus on the 'master immune regulator' nuclear factor kappa B (NF-κB) and review evidence in support of NF-κB dysregulation causing or contributing to neuroinflammation in patients. We discuss the utility of 'immune biotyping' as a tool to analyse immune-related transcripts and proteins in patient tissue, and the insights into cortical NF-κB in schizophrenia revealed by immune biotyping compared to studies treating patients as a single, homogenous group. Though the ubiquitous nature of NF-κB presents several hurdles for drug development, targeting this key immunoregulator with novel or repurposed therapeutics in schizophrenia is a relatively underexplored area that could aid in reducing symptoms of patients with active neuroinflammation.

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.

Meta-Analysis of Cytokine and Chemokine Genes in Schizophrenia

INTRODUCTION

Immune system genes, including cytokines, are associated with schizophrenia risk. Polymorphisms in cytokine genes may also impact on blood levels of cytokines, which are altered in patients with schizophrenia. We performed a meta-analysis of case-control studies of cytokine and chemokine genes in schizophrenia that have not been considered in previous quantitative reviews.

METHODS

We identified articles by systematic searches of PubMed, PsycInfo, and ISI, and the reference lists of identified studies. For each cytokine or chemokine polymorphism, we performed an allele- and genotype-wise meta-analysis, using a random effects model.

RESULTS

Twenty-one independent studies met the inclusion criteria, comprising polymorphisms for the IL1B, IL2, IL4, IL6, sIL6R, MCP1, and TGFB1 genes. For IL6, the A allele (OR=0.95, 95% CI 0.91-0.99) and AA genotype (OR=0.65, 95% CI 0.50-0.85) for the rs1800795 polymorphism, and for sIL6R, the A allele (OR=0.96 95%, CI 0.92-1.00) and AA genotype (OR=0.72, 95% CI 0.55-0.94) the rs8192284 polymorphism were associated with significantly decreased schizophrenia risk. In the genotype-wise analysis for IL1B, homozygosity for either allele (AA: OR=1.91, 95% CI 1.60-2.27; and GG: OR=0.40, 95% CI 0.33-0.49) of the rs1143627 polymorphism was also significantly associated with schizophrenia risk.

CONCLUSIONS

Associations between polymorphisms for the IL1B, IL6, and sIL6R genes and schizophrenia risk complement and extend previous findings regarding immune dysfunction in this disorder, including genome-wide association studies. Future studies of cytokine expression in schizophrenia should consider the effect of these polymorphisms. The finding of potential "protective" alleles may also be relevant for at-risk populations.

Association study of functional polymorphisms in interleukins and interleukin receptors genes: IL1A, IL1B, IL1RN, IL6, IL6R, IL10, IL10RA and TGFB1 in schizophrenia in Polish population

Schizophrenia has been associated with a large range of autoimmune diseases, with a history of any autoimmune disease being associated with a 45% increase in risk for the illness. The inflammatory system may trigger or modulate the course of schizophrenia through complex mechanisms influencing neurodevelopment, neuroplasticity and neurotransmission. In particular, increases or imbalance in cytokine before birth or during the early stages of life may affect neurodevelopment and produce vulnerability to the disease. A total of 27 polymorphisms of IL1N gene: rs1800587, rs17561; IL1B gene: rs1143634, rs1143643, rs16944, rs4848306, rs1143623, rs1143633, rs1143627; IL1RN gene: rs419598, rs315952, rs9005, rs4251961; IL6 gene: rs1800795, rs1800797; IL6R gene: rs4537545, rs4845617, rs2228145, IL10 gene: rs1800896, rs1800871, rs1800872, rs1800890, rs6676671; IL10RA gene: rs2229113, rs3135932; TGF1B gene: rs1800469, rs1800470; each selected on the basis of molecular evidence for functionality, were investigated in this study. Analysis was performed on a group of 621 patients with diagnosis of schizophrenia and 531 healthy controls in Polish population. An association of rs4848306 in IL1B gene, rs4251961 in IL1RN gene, rs2228145 and rs4537545 in IL6R with schizophrenia have been observed. rs6676671 in IL10 was associated with early age of onset. Strong linkage disequilibrium was observed between analyzed polymorphisms in each gene, except of IL10RA. We observed that haplotypes composed of rs4537545 and rs2228145 in IL6R gene were associated with schizophrenia. Analyses with family history of schizophrenia, other psychiatric disorders and alcohol abuse/dependence did not show any positive findings. Further studies on larger groups along with correlation with circulating protein levels are needed.

A functional polymorphism in the interleukin-1beta and severity of nicotine dependence in male schizophrenia: a case-control study

Previous studies have shown that the functional 511C/T polymorphism in the IL-1beta-gene may be implicated in the susceptibility for schizophrenia. Moreover, recent studies suggested that IL-1 participates in the progression of lung disease in smokers, which are overrepresented in schizophrenia. We aimed to investigate the possible relationship between the IL-1beta-511C/T polymorphism and smoking behavior in schizophrenia versus healthy controls in a Chinese population. The IL-1beta-511C/T polymorphism was genotyped in 638 male patients with chronic schizophrenia (smoker/never-smoker = 486/152) and 469 male controls (smoker/never-smoker = 243/226). The cigarettes smoked per day, the Heaviness of Smoking Index (HSI) and the Fagerstrom Test for nicotine dependence (FTND) were assessed. Patients were also rated on the Positive and Negative Syndrome Scale (PANSS). The results showed no significant differences in genotype and allele distribution between patients and controls, and between smokers and never-smokers in either the patient or control group. However, in patients, smokers with the C/C genotype had significantly higher HSI (p < 0.005) and FTND (p < 0.05) scores than smokers with the T/T genotype, without significant differences in controls. Furthermore, there was a linear positive correlation between the number of C alleles and the HSI (p < 0.005) in patients. Our findings suggest that the IL-1beta-511C/T polymorphism may not be related to schizophrenia or smoking status in Chinese individuals, but may affect the severity of nicotine dependence among male smokers with schizophrenia.

Evidence for a dysregulated immune system in the etiology of psychiatric disorders

There is extensive bi-directional communication between the brain and the immune system in both health and disease. In recent years, the role of an altered immune system in the etiology of major psychiatric disorders has become more apparent. Studies have demonstrated that some patients with major psychiatric disorders exhibit characteristic signs of immune dysregulation and that this may be a common pathophysiological mechanism that underlies the development and progression of these disorders. Furthermore, many psychiatric disorders are also often accompanied by chronic medical conditions related to immune dysfunction such as autoimmune diseases, diabetes and atherosclerosis. One of the major psychiatric disorders that has been associated with an altered immune system is schizophrenia, with approximately one third of patients with this disorder showing immunological abnormalities such as an altered cytokine profile in serum and cerebrospinal fluid. An altered cytokine profile is also found in a proportion of patients with major depressive disorder and is thought to be potentially related to the pathophysiology of this disorder. Emerging evidence suggests that altered immune parameters may also be implicated in the neurobiological etiology of autism spectrum disorders. Further support for a role of immune dysregulation in the pathophysiology of these psychiatric disorders comes from studies showing the immunomodulating effects of antipsychotics and antidepressants, and the mood altering effects of anti-inflammatory therapies. This review will not attempt to discuss all of the psychiatric disorders that have been associated with an augmented immune system, but will instead focus on several key disorders where dysregulation of this system has been implicated in their pathophysiology including depression, schizophrenia and autism spectrum disorder.

Effect of the interleukin-1β gene on dorsolateral prefrontal cortex function in schizophrenia: a genetic neuroimaging study

BACKGROUND

Genetic studies have found that the interleukin-1β gene (IL1B, 2q13) influences the risk for schizophrenia, but the underlying biological mechanisms of the association are still unclear. Investigation of the effects of genetic variability in this gene on brain function could provide more information about its role in the disorder.

METHODS

The present study examined the effects of a functional polymorphism at IL1B gene promoter (-511C/T; rs16944) on brain correlates of working memory performance in schizophrenia. Forty-eight schizophrenia patients and 46 control subjects underwent functional magnetic resonance imaging while performing the n-back task.

RESULTS

In the pooled sample, genetic variability at this locus was associated with differential brain activation in a bilateral frontal region including the dorsolateral prefrontal cortex. There was also a significant diagnosis × genotype interaction effect in an overlapping frontal region: the IL1B polymorphism did not affect activation in the control subjects in this area, but the schizophrenia patients who were T carriers showed significantly higher activation than the CC homozygotes.

CONCLUSIONS

The findings support a role for IL1B variability in the dorsolateral prefrontal cortex dysfunction classically associated with schizophrenia.

Haplotypes in the expression quantitative trait locus of interleukin-1β gene are associated with schizophrenia

Recent genome-wide association study (GWAS) and gene expression analyses have revealed that single nucleotide polymorphisms (SNPs) associated with complex diseases such as schizophrenia are significantly more likely to be associated with expression quantitative trait loci (eQTL). The interleukin-1β (IL1B) gene has been strongly implicated in the susceptibility to schizophrenia. In order to test this association, we selected five tag SNPs in the eQTL of the IL1B gene and conducted a case-control study using two independent samples. The first sample comprised 528 schizophrenic patients and 709 controls and the second sample comprised 576 schizophrenic patients and 768 controls. We identified two SNPs and several haplotypes as being significantly associated with schizophrenia. Previous reports indicated that one major haplotype that was protective against schizophrenia reduced IL1B transcription, while two risk haplotypes for schizophrenia enhanced IL1B transcription. Therefore, we measured IL1B mRNA expression in PAXgene-stabilized whole blood from 40 schizophrenic patients and 40 controls to explore the possibility of using five tag SNPs as schizophrenic trait markers. A multiple regression analysis taking confounding factors into account revealed that the T allele of rs4848306 SNP, which is a protective allele for schizophrenia, predicted reduced change in IL1B mRNA expression, regardless of phenotype. Our results appear to support the previous hypothesis that IL1B contributes to the genetic risk of schizophrenia and warrant further research on the association of eQTL SNPs with schizophrenia.

Convergent evidence shows a positive association of interleukin-1 gene complex locus with susceptibility to schizophrenia in the Caucasian population

Recent genetic studies have revealed that the Interleukin-1 (IL1) gene complex (IL1 alpha, IL1 beta and IL1 receptor antagonist) is associated with schizophrenia, but contradictory findings have also been reported. We investigated the association of the IL1 gene complex locus and schizophrenia using meta-analytic techniques, covering all published data up to January 2010, to restrict to the most commonly reported 4 single nucleotide polymorphisms (SNP). We also explored potential sources of heterogeneity and to investigate whether ancestry and study design moderated any association. The combined allele-wise odds ratio (OR) for schizophrenia of the rs16944 (IL1B gene; T-511C) polymorphism was 0.86 (95% CI: 0.77to 0.96).When applying stratified analysis to this polymorphism, the pooled allele-wise OR was 0.88 (95% CI, 0.79 to 0.97) in 10 population-based studies and 0.85 (95% CI: 0.73 to 0.99) in Caucasian samples. In a stratified analysis of the rs1143634 (IL1B gene; T3953C) polymorphism, the pooled genotype-wise results in a dominant model were also statistically significant both in a population-based study subgroup with summary OR of 0.64 (95% CI: 0.41 to 0.99) and a Caucasian population subgroup with summary OR of 0.62 (95% CI: 0.40 to 0.97). Neither combined nor stratified analyses found any association of the rs1800587 (IL1A gene; T-889C) or rs1794068 (IL1RA Gene; IL1RN_86 bp; T/C) with schizophrenia susceptibility. Our study suggests the IL1B gene or the IL1 gene complex may play a moderate role in the etiology of schizophrenia in the Caucasian population.

Lack of association between the interleukin-1 gene complex and schizophrenia in a Japanese population

Interleukin-1 (IL1) is an inflammatory cytokine and exerts neurodegenerative effects in the brain. Several studies have indicated that IL1 is likely to be involved in the pathogenesis of schizophrenia. Recent genetic studies have revealed that the IL1 gene complex (IL,1 alpha, IL1, beta and IL1 receptor antagonist) was associated with schizophrenia, although contradictory findings have also been reported. To assess whether the IL1 gene complex was implicated in vulnerability to schizophrenia, the authors conducted a case-control association study (416 patients with schizophrenia and 440 control subjects) for nine polymorphisms in Japanese subjects. The authors found no association between the IL1 gene complex polymorphisms and schizophrenia using either single-marker or haplotype analyses. The results of the present study suggest that the IL1 gene complex does not play a major role in conferring susceptibility to schizophrenia in the Japanese population.