The complement system in schizophrenia

Sex-dependent association study of complement C4 gene with treatment-resistant schizophrenia and hospitalization frequency

The complement component 4 (C4) gene, codes for two isotypes, C4A and C4B, and can exist in long or short forms (C4L and C4S). The C4AL variant has been associated with elevated schizophrenia (SCZ) risk. Here, we investigated the relationship between C4 variation and clinical outcomes in SCZ. N = 434 adults with SCZ or schizoaffective disorder were included in this retrospective study. A three-step genotyping workflow was performed to determine C4 copy number variants. These variants were tested for association with clinical outcome measures, including treatment-resistant SCZ (TRS), number of hospitalizations (NOH), and symptom severity (PANSS). Sex and ancestry stratified analyses were performed. We observed a marginally significant association between C4S and TRS in males only, and a negative association between C4S and NOH in the total sample. C4AS had negative association with NOH in males and non-Europeans. Lastly, C4A copy numbers and C4A predicted brain expression showed negative association with NOH in males only. Our study provides further support for sex-specific effect of C4 on SCZ clinical outcomes, and also suggests that C4S and C4AS might have a protective effect against increased severity. C4 could potentially serve as a genetic biomarker in the future, however, more research is required.

Analysis of the complement component C4 gene with schizophrenia subphenotypes

BACKGROUND

The complement component C4 gene has been identified as a strong marker for schizophrenia (SCZ) risk. The C4 gene has a complex genetic structure consisting of variable structural elements (C4A, C4B, C4L, and C4S) and compound structural forms (C4AL, C4BL, C4AS and C4BS). In addition, the variations in C4 structural forms may have a direct or indirect effect on the brain expression level of C4A and C4B proteins. Previous studies have associated C4AL with higher brain C4A expression and sex-dimorphism of C4 between males and females was observed.

STUDY DESIGN

A total of 613 patients with DSM-IV SCZ or schizoaffective disorder (SCZ-AFF) were recruited to investigate the relationship between C4 gene variants and clinical characteristics of SCZ (age of onset, symptom severity, and global assessment of functioning (GAF)). This study also explored the effect of sex on the association of C4 with SCZ. 434 patients were included in the final analyses after genetic quality control.

RESULTS

We observed associations between C4 and clinical characteristics of SCZ (age of onset, symptom severity, GAF) and found significant differences when males and females were examined separately.

CONCLUSION

Overall, our preliminary findings encourage future investigations of C4 in SCZ-related phenotypes, including antipsychotic response and side effects. The study sample was of moderate size; therefore, further studies in larger samples are needed to extend and validate these results.

Soluble terminal complement complex blood levels are elevated in schizophrenia

The role of the complement system in schizophrenia (Sz) is inconclusive due to heterogeneity of the disease and study designs. Here, we assessed the levels of complement activation products and functionality of the classical pathway in acutely ill unmedicated Sz patients at baseline and after 6 weeks of treatment versus matched controls. The study included analyses of the terminal complement complex (sTCC) and C5a in plasma from 96 patients and 96 controls by enzyme-linked immunosorbent assay. Sub-group analysis of serum was conducted for measurement of C4 component and activity of the classical pathway (28 and 24 cases per cohort, respectively). We found no differences in levels of C5a, C4 and classical pathway function in patients versus controls. Plasma sTCC was significantly higher in patients [486 (392-659) ng/mL, n = 96] compared to controls [389 (304-612) ng/mL, n = 96] (p = 0.027, δ = 0.185), but not associated with clinical symptom ratings or treatment. The differences in sTCC between Sz and controls were confirmed using an Aligned Rank Transformation model considering the covariates age and sex (p = 0.040). Additional analysis showed that sTCC was significantly associated with C-reactive protein (CRP; p = 0.006). These findings suggest that sTCC plays a role in Sz as a trait marker of non-specific chronic immune activation, as previously described for CRP. Future longitudinal analyses with more sampling time points from early recognition centres for psychoses may be helpful to better understand the temporal dynamics of innate immune system changes during psychosis development.

The complement system in neurodegenerative and inflammatory diseases of the central nervous system

Neurodegenerative and neuroinflammatory diseases, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis, affect millions of people globally. As aging is a major risk factor for neurodegenerative diseases, the continuous increase in the elderly population across Western societies is also associated with a rising prevalence of these debilitating conditions. The complement system, a crucial component of the innate immune response, has gained increasing attention for its multifaceted involvement in the normal development of the central nervous system (CNS) and the brain but also as a pathogenic driver in several neuroinflammatory disease states. Although complement is generally understood as a liver-derived and blood or interstitial fluid operative system protecting against bloodborne pathogens or threats, recent research, particularly on the role of complement in the healthy and diseased CNS, has demonstrated the importance of locally produced and activated complement components. Here, we provide a succinct overview over the known beneficial and pathological roles of complement in the CNS with focus on local sources of complement, including a discussion on the potential importance of the recently discovered intracellularly active complement system for CNS biology and on infection-triggered neurodegeneration.

Microglia-neuron interactions in schizophrenia

Multiple lines of evidence implicate increased neuroinflammation mediated by glial cells to play a key role in neurodevelopmental disorders such as schizophrenia. Microglia, which are the primary innate immune cells of the brain, are crucial for the refinement of the synaptic circuitry during early brain development by synaptic pruning and the regulation of synaptic plasticity during adulthood. Schizophrenia risk factors as genetics or environmental influences may further be linked to increased activation of microglia, an increase of pro-inflammatory cytokine levels and activation of the inflammasome resulting in an overall elevated neuroinflammatory state in patients. Synaptic loss, one of the central pathological hallmarks of schizophrenia, is believed to be due to excess removal of synapses by activated microglia, primarily affecting glutamatergic neurons. Therefore, it is crucial to investigate microglia-neuron interactions, which has been done by multiple studies focusing on post-mortem brain tissues, brain imaging, animal models and patient iPSC-derived 2D culture systems. In this review, we summarize the major findings in patients and in vivo and in vitro models in the context of neuron-microglia interactions in schizophrenia and secondly discuss the potential of anti-inflammatory treatments for the alleviation of positive, negative, and cognitive symptoms.

Association study of the complement component C4 gene and suicide risk in schizophrenia

Schizophrenia is a severe mental illness and a major risk factor for suicide, with approximately 50% of schizophrenia patients attempting and 10% dying from suicide. Although genetic components play a significant role in schizophrenia risk, the underlying genetic risk factors for suicide are poorly understood. The complement component C4 gene, an immune gene involved in the innate immune system and located in the major histocompatibility complex (MHC) region, has been identified to be strongly associated with schizophrenia risk. In addition, recent findings have also suggested that the MHC region has been associated with suicide risk across disorders, making C4 a potential candidate of interest for studying suicidality in schizophrenia patients. Despite growing interest in investigating the association between the C4 gene and schizophrenia, to our knowledge, no work has been done to examine the potential of C4 variants as suicide risk factors in patients with schizophrenia. In this study, we investigated the association between different C4 copy number variants and predicted C4 brain expression with suicidal outcomes (suicide attempts/suicidal ideation). We directly genotyped 434 schizophrenia patients to determine their C4A and C4B copy number variants. We found the C4AS copy number to be marginally and negatively associated with suicide risk, potentially being protective against suicide attempts (OR = 0.49; p = 0.05) and suicidal ideation (OR = 0.65; p = 0.07). Furthermore, sex-stratified analyses revealed that there are no significant differences between males and females. Our preliminary findings encourage additional studies of C4 and potential immune dysregulation in suicide.

The correlates of neonatal complement component 3 and 4 protein concentrations with a focus on psychiatric and autoimmune disorders

Complement components have been linked to schizophrenia and autoimmune disorders. We examined the association between neonatal circulating C3 and C4 protein concentrations in 68,768 neonates and the risk of six mental disorders. We completed genome-wide association studies (GWASs) for C3 and C4 and applied the summary statistics in Mendelian randomization and phenome-wide association studies related to mental and autoimmune disorders. The GWASs for C3 and C4 protein concentrations identified 15 and 36 independent loci, respectively. We found no associations between neonatal C3 and C4 concentrations and mental disorders in the total sample (both sexes combined); however, post-hoc analyses found that a higher C3 concentration was associated with a reduced risk of schizophrenia in females. Mendelian randomization based on C4 summary statistics found an altered risk of five types of autoimmune disorders. Our study adds to our understanding of the associations between C3 and C4 concentrations and subsequent mental and autoimmune disorders.

Prospects and Pitfalls of Plasma Complement C4 in Schizophrenia: Building a Better Biomarker

Complex brain disorders like schizophrenia may have multifactorial origins related to mis-timed heritable and environmental factors interacting during neurodevelopment. Infections, inflammation, and autoimmune diseases are over-represented in schizophrenia leading to immune system-centered hypotheses. Complement component C4 is genetically and neurobiologically associated with schizophrenia, and its dual activity peripherally and in the brain makes it an exceptional target for biomarker development. Studies to evaluate the biomarker potential of plasma or serum C4 in schizophrenia do so to understand how peripheral C4 might reflect central nervous system-derived neuroinflammation, synapse pruning, and other mechanisms. This effort, however, has produced mostly conflicting results, with peripheral C4 sometimes elevated, reduced, or unchanged between comparison groups. We undertook a pilot biomarker development study to systematically identify sociodemographic, genetic, and immune-related variables (autoimmune, infection-related, gastrointestinal, inflammatory), which may be associated with plasma C4 levels in schizophrenia (SCH; n = 335) and/or in nonpsychiatric comparison subjects (NCs; n = 233). As with previously inconclusive studies, we detected no differences in plasma C4 levels between SCH and NCs. In contrast, levels of general inflammation, C-reactive protein (CRP), were significantly elevated in SCH compared to NCs (ANOVA, F = 20.74, p < 0.0001), suggestive that plasma C4 and CRP may reflect different sources or causes of inflammation. In multivariate regressions of C4 gene copy number variants, plasma C4 levels were correlated only for C4A (not C4B, C4L, C4S) and only in NCs (R Coeff = 0.39, CI = 0.01-0.77, R2 = 0.18, p < 0.01; not SCH). Other variables associated with plasma C4 levels only in NCs included sex, double-stranded DNA IgG, tissue-transglutaminase (TTG) IgG, and cytomegalovirus IgG. Toxoplasma gondii IgG was the only variable significantly correlated with plasma C4 in SCH but not in NCs. Many variables were associated with plasma C4 in both groups (body mass index, race, CRP, N-methyl-D-aspartate receptor (NMDAR) NR2 subunit IgG, TTG IgA, lipopolysaccharide-binding protein (LBP), and soluble CD14 (sCD14). While the direction of most C4 associations was positive, autoimmune markers tended to be inverse, and associated with reduced plasma C4 levels. When NMDAR-NR2 autoantibody-positive individuals were removed, plasma C4 was elevated in SCH versus NCs (ANOVA, F = 5.16, p < 0.02). Our study was exploratory and confirmation of the many variables associated with peripheral C4 requires replication. Our preliminary results point toward autoimmune factors and exposure to the pathogen, T. gondii, as possibly significant contributors to variability of total C4 protein levels in plasma of individuals with schizophrenia.

Inflammation-Related Functional and Structural Dysconnectivity as a Pathway to Psychopathology

Findings from numerous laboratories and across neuroimaging modalities have consistently shown that exogenous administration of cytokines or inflammatory stimuli that induce cytokines disrupts circuits and networks involved in motivation and motor activity, threat detection, anxiety, and interoceptive and emotional processing. While inflammatory effects on neural circuits and relevant behaviors may represent adaptive responses promoting conservation of energy and heightened vigilance during immune activation, chronically elevated inflammation may contribute to symptoms of psychiatric illnesses. Indeed, biomarkers of inflammation such as cytokines and acute phase reactants are reliably elevated in a subset of patients with unipolar or bipolar depression, anxiety-related disorders, and schizophrenia and have been associated with differential treatment responses and poor clinical outcomes. A growing body of literature also describes higher levels of endogenous inflammatory markers and altered, typically lower functional or structural connectivity within these circuits in association with transdiagnostic symptoms such as anhedonia and anxiety in psychiatric and at-risk populations. This review presents recent evidence that inflammation and its effects on the brain may serve as one molecular and cellular mechanism of dysconnectivity within anatomically and/or functionally connected cortical and subcortical regions in association with transdiagnostic symptoms. We also discuss the need to establish reproducible methods to assess inflammation-associated dysconnectivity in relation to behavior for use in translational studies or biomarker-driven clinical trials for novel pharmacological or behavioral interventions targeting inflammation or its effects on the brain.

Complement Activation Products in Patients with Chronic Schizophrenia

Evidence suggests a role of the immune system in the pathogenesis of a number of mental conditions, including schizophrenia (SCH). In terms of physiology, aside from its crucial protective function, the complement cascade (CC) is a critical element of the regeneration processes, including neurogenesis. Few studies have attempted to define the function of the CC components in SCH. To shed more light on this topic, we compared the levels of complement activation products (CAP) (C3a, C5a and C5b-9) in the peripheral blood of 62 patients with chronic SCH and disease duration of ≥ 10 years with 25 healthy controls matched for age, sex, BMI and smoking status. Concentrations of all the investigated CAP were elevated in SCH patients. However, after controlling for potential confounding factors, significant correlations were observed between SCH and C3a (M = 724.98 ng/mL) and C5a (M = 6.06 ng/mL) levels. In addition, multivariate logistic regression showed that C3a and C5b-9 were significant predictors of SCH. There were no significant correlations between any CAP and SCH symptom severity or general psychopathology in SCH patients. However, two significant links emerged between C3a and C5b-9 and global functioning. Increased levels of both complement activation products in the patient group as compared to healthy controls raise questions concerning the role of the CC in the etiology of SCH and further demonstrate dysregulation of the immune system in SCH patients.

Consolidation of metabolomic, proteomic, and GWAS data in connective model of schizophrenia

Despite of multiple systematic studies of schizophrenia based on proteomics, metabolomics, and genome-wide significant loci, reconstruction of underlying mechanism is still a challenging task. Combination of the advanced data for quantitative proteomics, metabolomics, and genome-wide association study (GWAS) can enhance the current fundamental knowledge about molecular pathogenesis of schizophrenia. In this study, we utilized quantitative proteomic and metabolomic assay, and high throughput genotyping for the GWAS study. We identified 20 differently expressed proteins that were validated on an independent cohort of patients with schizophrenia, including ALS, A1AG1, PEDF, VTDB, CERU, APOB, APOH, FASN, GPX3, etc. and almost half of them are new for schizophrenia. The metabolomic survey revealed 18 group-specific compounds, most of which were the part of transformation of tyrosine and steroids with the prevalence to androgens (androsterone sulfate, thyroliberin, thyroxine, dihydrotestosterone, androstenedione, cholesterol sulfate, metanephrine, dopaquinone, etc.). The GWAS assay mostly failed to reveal significantly associated loci therefore 52 loci with the smoothened p < 10^-5 were fractionally integrated into proteome-metabolome data. We integrated three omics layers and powered them by the quantitative analysis to propose a map of molecular events associated with schizophrenia psychopathology. The resulting interplay between different molecular layers emphasizes a strict implication of lipids transport, oxidative stress, imbalance in steroidogenesis and associated impartments of thyroid hormones as key interconnected nodes essential for understanding of how the regulation of distinct metabolic axis is achieved and what happens in the conditioned proteome and metabolome to produce a schizophrenia-specific pattern.

Dysregulation of complement system in neuropsychiatric disorders: A mini review

Complement system is one of the most important defense mechanisms of the innate immune system. In addition to their roles in immune regulation, complement proteins are also involved in neurodevelopment and adult brain plasticity. Complement dysregulation has been shown in neurodevelopmental disorders including schizophrenia and autism spectrum disorder as well as in mood disorders. A number of clinical as well as genetic studies suggest the role of complement proteins in the cortical thinning and excessive synaptic pruning frequently associated with schizophrenia. The changes in complement proteins are also associated with the pathophysiology of autism spectrum disorder, major depressive disorder and bipolar disorder, but warrant further research. In addition, rodent models suggest a strong case for complement system in anxiety-like behavior. In this article, we review the recent findings on the role of complement system in neuropsychiatric disorders. The possible uses for future complement targeted therapies are also discussed.

The acute effects of antimicrobials and lipopolysaccharide on the cellular mechanisms associated with neurodegeneration in pubertal male and female CD1 mice

Exposure to stressors during puberty can cause enduring effects on brain functioning and behaviours related to neurodegeneration. However, the mechanisms underlying these effects remain unclear. The gut microbiome is a complex and dynamic system that could serve as a possible mechanism through which early life stress may increase the predisposition to neurodegeneration. Therefore, the current study was designed to examine the acute effects of pubertal antimicrobial and lipopolysaccharide (LPS) treatments on the cellular mechanisms associated with neurodegenerative disorders in male and female mice. At five weeks of age, male and female CD-1 mice received 200 μL of broad-spectrum antimicrobials or water, through oral gavage, twice daily for seven days. Mice received an intraperitoneal (i.p.) injection of either saline or LPS at 6 weeks of age (i.e., pubertal period). Sickness behaviours were recorded and mice were euthanized 8 h post-injection. Following euthanasia, brains and blood samples were collected. The results indicated that puberal antimicrobial and LPS treatment induced sex-dependent changes in biomarkers related to sickness behaviour, peripheral inflammation, intestinal permeability, and neurodegeneration. The findings suggest that pubertal LPS and antimicrobial treatment may increase susceptibility to neurodegenerative diseases later in life, particularly in males.

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Pubertal antimicrobial and LPS treatment increase cytokine concentrations.

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Antimicrobial and LPS treatment have sex-specific effects on intestinal permeability.

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They also induce sex-specific changes in neurodegenerative markers.

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Antimicrobial treatment did not potentiate LPS-induced sickness behaviours.

Multifaceted Activities of Seven Nanobodies against Complement C4b

Cleavage of the mammalian plasma protein C4 into C4b initiates opsonization, lysis, and clearance of microbes and damaged host cells by the classical and lectin pathways of the complement system. Dysregulated activation of C4 and other initial components of the classical pathway may cause or aggravate pathologies, such as systemic lupus erythematosus, Alzheimer disease, and schizophrenia. Modulating the activity of C4b by small-molecule or protein-based inhibitors may represent a promising therapeutic approach for preventing excessive inflammation and damage to host cells and tissue. Here, we present seven nanobodies, derived from llama (Lama glama) immunization, that bind to human C4b (Homo sapiens) with high affinities ranging from 3.2 nM to 14 pM. The activity of the nanobodies varies from no to complete inhibition of the classical pathway. The inhibiting nanobodies affect different steps in complement activation, in line with blocking sites for proconvertase formation, C3 substrate binding to the convertase, and regulator-mediated inactivation of C4b. For four nanobodies, we determined single-particle cryo-electron microscopy structures in complex with C4b at 3.4-4 Å resolution. The structures rationalize the observed functional effects of the nanobodies and define their mode of action during complement activation. Thus, we characterized seven anti-C4b nanobodies with diverse effects on the classical pathway of complement activation that may be explored for imaging, diagnostic, or therapeutic applications.

C-Reactive Protein: Marker of risk for post-traumatic stress disorder and its potential for a mechanistic role in trauma response and recovery

Increasing evidence indicates that inflammation plays a role in PTSD and stress disorder pathophysiology. PTSD is consistently associated with higher circulating inflammatory protein levels. Rodent models demonstrate that inflammation promotes enduring avoidance and arousal behaviors after severe stressors (e.g., predator exposure and social defeat), suggesting that inflammation may play a mechanistic role in trauma disorders. C-reactive protein (CRP) is an innate acute phase reactant produced by the liver after acute infection and chronic disease. A growing number of investigations report associations with PTSD diagnosis and elevated peripheral CRP, CRP gene mutations, and CRP gene expression changes in immune signaling pathways. CRP is reasonably established as a potential marker of PTSD and trauma exposure, but if and how it may play a mechanistic role is unclear. In this review, we discuss the current understanding of immune mechanisms in PTSD with a particular focus on the innate immune signaling factor, CRP. We found that although there is consistent evidence of an association of CRP with PTSD symptoms and risk, there is a paucity of data on how CRP might contribute to CNS inflammation in PTSD, and consequently, PTSD symptoms. We discuss potential mechanisms through which CRP could modulate enduring peripheral and CNS stress responses, along with future areas of investigation probing the role of CRP and other innate immune signaling factors in modulating trauma responses. Overall, we found that CRP likely contributes to central inflammation, but how it does so is an area for further study.

Schizophrenia risk loci from xMHC region were associated with antipsychotic response in chronic schizophrenic patients with persistent positive symptom

We examined whether common variants from the extended major histocompatibility complex (xMHC) region contribute to the response to antipsychotic drugs (APDs) in patients with schizophrenia with persistent psychosis. Subjects participated in a prospective longitudinal study of the effect of APDs on psychopathology were temporally split into discovery (n = 88) and replication (n = 42) cohorts. The primary endpoint was a change in Brief Psychiatric Rating Scale at 6-week or 6-month after treatment. rs204991 (β = 3.917, p = 3.72 × 10^-6), the strongest signal associated with response at 6-week was located near C4A/C4B after a linear regression adjusted for covariates. xMHC SNP imputation disclosed much stronger signals (rs9268469, β = 5.140, p = 1.57 × 10^-7) and other weaker signals (p < 1 × 10^-5) spanning the entire xMHC region. All the variants were previously identified schizophrenia risk loci. Conditional fine-mapping revealed three subgroups of SNPs which were the eQTLs (p < 1 × 10^-7) for C4A, HLA-C, and BTN3A2 in disease-relevant tissue. Epistasis between HLA-C and C4A was observed (p = 0.019). Minor allele (G) carriers of rs204991, eQTL for C4A, having decreased risk for schizophrenia and lower imputed expression of C4A, had a better response to APDs. Some imputed HLA alleles associated with a decreased risk for schizophrenia had a positive association with improvement in psychotic symptoms. An independent cohort validated the association of change in psychosis with C4A. We provide evidence that genetic risk factors for schizophrenia from the xMHC region are associated with response to APDs and those variants significantly alter the imputed expression of C4A, HLA-C, and BTN3A2. The minor alleles predicting higher C4A level are associated with diminished improvement in psychotic symptoms after APD treatment.

Peripheral complement is increased in schizophrenia and inversely related to cortical thickness

BACKGROUND

There is growing evidence for complement system involvement in the pathophysiology of schizophrenia, although the extent and magnitude of complement factor disturbances has not been fully reported. It also remains unclear whether complement abnormalities are characteristic of all patients with schizophrenia or whether they are representative of a subgroup of patients who show signs of heightened inflammation. The aim of the present study was to quantify and compare the levels of a range of complement factors, receptors and regulators in healthy controls and people with schizophrenia and to determine the extent to which the levels of these peripheral molecules relate to measures of brain structure, particularly cortical thickness.

METHOD

Seventy-five healthy controls and 90 patients with schizophrenia or schizoaffective disorder were included in the study. Peripheral blood samples were collected from all participants and mRNA expression was quantified in 20 complement related genes, four complement proteins, as well as for four cytokines. T1-weighted structural MRI scans were acquired and analysed to determine cortical thickness measures.

RESULTS

There were significant increases in peripheral mRNA encoding receptors (C5ar1, CR1, CR3a), regulators (CD55, C59) and protein concentrations (C3, C3b, C4) in people with schizophrenia relative to healthy controls. C4a expression was significantly increased in a subgroup of patients displaying elevated peripheral cytokine levels. A higher inflammation index score derived from mRNA expression patterns predicted reductions in cortical thickness in the temporal lobe (superior temporal gyrus, transverse temporal gyrus, fusiform gyrus, insula) in patients with schizophrenia and healthy controls.

CONCLUSIONS

Analysis of all three major complement pathways supports increased complement activity in schizophrenia and also shows that peripheral C4a up-regulation is related to increased peripheral pro-inflammatory cytokines in healthy controls. Our region-specific, neuroimaging findings linked to an increased peripheral complement mRNA expression pattern suggests a role for complement in cortical thinning. Further studies are required to further clarify clinical and neurobiological consequences of aberrant complement levels in schizophrenia and related psychoses.

Deregulation of complement components C4A and CSMD1 peripheral expression in first-episode psychosis and links to cognitive ability

Up-regulation of the complement component 4A (C4A) in the brain has been associated with excessive synaptic pruning and increased schizophrenia (SZ) susceptibility. Over-expression of C4A has been observed in SZ postmortem brain tissue, and the gene encoding for a protein inhibitor of C4A activity, CUB and Sushi multiple domains 1 (CSMD1) gene, has been implicated in SZ risk and cognitive ability. Herein, we examined C4A and CSMD1 mRNA expression in peripheral blood from antipsychotic-naive individuals with first-episode psychosis (FEP; n = 73) and mentally healthy volunteers (n = 48). Imputed C4 locus structural alleles and C4A serum protein levels were investigated. Associations with symptom severity and cognitive domains performance were explored. A significant decrease in CSMD1 expression levels was noted among FEP patients compared to healthy volunteers, further indicating a positive correlation between C4A and CSMD1 mRNA levels in healthy volunteers but not in FEP cases. In addition, C4 copy number variants previously associated with SZ risk correlated with higher C4A mRNA levels in FEP cases, which confirms the regulatory effect of C4 structural variants on gene expression. Evidence also emerged for markedly elevated C4A serum concentrations in FEP cases. Within the FEP patient group, higher C4A mRNA levels correlated with more severe general psychopathology symptoms and lower CSMD1 mRNA levels predicted worse working memory performance. Overall, these findings suggest C4A complement pathway perturbations in individuals with FEP and corroborate the involvement of CSMD1 in prefrontal-mediated cognitive functioning.

Methodological Appraisal of Literature Concerning the Analysis of Genetic Variants or Protein Levels of Complement Components on Susceptibility to Infection by Trypanosomatids: A Systematic Review

Background

Trypanosomatids are protozoa responsible for a wide range of diseases, with emphasis on Chagas Disease (CD) and Leishmaniasis, which are in the list of most relevant Neglected Tropical Diseases (NTD) according to World Health Organization (WHO). During the infectious process, immune system is immediately activated, and parasites can invade nucleated cells through a broad diversity of receptors. The complement system − through classical, alternative and lectin pathways − plays a role in the first line of defense against these pathogens, acting in opsonization, phagocytosis and lysis of parasites. Genetic modifications in complement genes, such as Single Nucleotide Polymorphisms (SNPs), can influence host susceptibility to these parasites and modulate protein expression.

Methods

In March and April 2021, a literature search was conducted at the PubMed and Google Scholar databases and the reference lists obtained were verified. After applying the inclusion and exclusion criteria, the selected studies were evaluated and scored according to eleven established criteria regarding their thematic approach and design, aiming at the good quality of publications.

Results

Twelve papers were included in this systematic review: seven investigating CD and five focusing on Leishmaniasis. Most articles presented gene and protein approaches, careful determination of experimental groups, and adequate choice of experimental techniques, although several of them were not up-to-date. Ten studies explored the association of polymorphisms and haplotypes with disease progression, with emphasis on lectin complement pathway genes. Decreased and increased patient serum protein levels were associated with susceptibility to CD and Visceral Leishmaniasis, respectively.

Conclusion

This systematic review shows the influence of genetic alterations in complement genes on the progression of several infectious diseases, with a focus on conditions caused by trypanosomatids, and contributes suggestions and evidence to improve experimental design in future research proposals.

Systemic lupus erythematosus and autoimmune features in chronic hospitalized patients with schizophrenia

OBJECTIVES

Recent studies highlighted the link of schizophrenia risk with genetic variations in complement, which share the same pathogenesis with systemic lupus erythematosus (SLE). However, the coexistence of SLE and schizophrenia were rarely reported. We aimed to explore the autoantibody profiles, complement levels and prevalence of SLE in chronic schizophrenia patients.

METHODS

A prospective, cross-sectional study was conducted to recruit 481 long-term hospitalized schizophrenia spectrum disorder patients in Yuli hospital, Taiwan. Severity of schizophrenia was assessed by Positive and Negative Syndrome Scale (PANSS). Immunologic tests of autoantibodies and complement levels were measured. Genome-wide association analysis was conducted to compare genetic variants between schizophrenia with SLE and non-SLE schizophrenia.

RESULTS

In total, 47 (9.8%) and 31 (6.4%) participants had positive anti-nuclear antibody (ANA) and anti-double stranded DNA (anti-dsDNA) antibodies, respectively. After rheumatologic exams, 30 (6.2%) patients were diagnosed schizophrenia with SLE, while 32 (6.7%) subjects were classified as schizophrenia with autoimmune features. Schizophrenia patients with SLE had more arthritis, serositis, homogenous ANA pattern, conceptual disorganization in PANSS and increased salivation due to psychotropics compared with their counterparts. ANA titers and complement levels were significantly correlated with PANSS scores and side effect of psychotropics. No significant genetic variation between schizophrenia with SLE and non-SLE schizophrenia were identified.

CONCLUSION

SLE may coexist in chronic hospitalized schizophrenia. Complement levels could be a potential biomarker in schizophrenia patients. Considering the possible reversibility of psychotic features and adverse effects of antipsychotics, SLE with psychosis should be identified in patients with chronic hospitalized schizophrenia.

Pharmacotherapy of schizophrenia: immunological aspects and potential role of immunotherapy

INTRODUCTION

Schizophrenia is a complex disorder owing to diversity in clinical phenotypes, overlapping symptoms, and heterogeneous clinical presentation. Even after decades of research, the exact causative mechanisms of schizophrenia are not completely known. Recent evidence indicates the role of immune dysfunction in schizophrenia pathogenesis as observed from alteration in immune cells, increased activity of complement cascade, and development of autoantibodies against neurotransmitter receptors. Immunotherapy involving immunosuppressants and cytokine-targeting drugs, have shown promising results in several clinical studies and it demands further research in this area.

AREAS COVERED

Here, the authors review the immunopathogenesis of schizophrenia, limitations of conventional, and atypical antipsychotic drugs and the potential role and limitations of immunotherapeutic drugs in schizophrenia management.

EXPERT OPINION

Schizophrenia is a complex disorder and poses a challenge to the currently available treatment approaches. Nearly 30% schizophrenia patients exhibit minimal response toward conventional and atypical antipsychotic drugs. Immune system dysfunction plays an important part of schizophrenia pathophysiology and existing monoclonal antibody (mAb) drugs targeting specific components of the immune system are being repositioned in schizophrenia. The authors call upon public and private funders to facilitate urgent and rigorous research efforts in exploring potential role of immunotherapy in schizophrenia.

Increased activation product of complement 4 protein in plasma of individuals with schizophrenia

Structural variation in the complement 4 gene (C4) confers genetic risk for schizophrenia. The variation includes numbers of the increased C4A copy number, which predicts increased C4A mRNA expression. C4-anaphylatoxin (C4-ana) is a C4 protein fragment released upon C4 protein activation that has the potential to change the blood-brain barrier (BBB). We hypothesized that elevated plasma levels of C4-ana occur in individuals with schizophrenia (iSCZ). Blood was collected from 15 iSCZ with illness duration < 5 years and from 14 healthy controls (HC). Plasma C4-ana was measured by radioimmunoassay. Other complement activation products C3-ana, C5-ana, and terminal complement complex (TCC) were also measured. Digital-droplet PCR was used to determine C4 gene structural variation state. Recombinant C4-ana was added to primary brain endothelial cells (BEC) and permeability was measured in vitro. C4-ana concentration was elevated in plasma from iSCZ compared to HC (mean = 654 ± 16 ng/mL, 557 ± 94 respectively, p = 0.01). The patients also carried more copies of the C4AL gene and demonstrated a positive correlation between plasma C4-ana concentrations and C4A gene copy number. Furthermore, C4-ana increased the permeability of a monolayer of BEC in vitro. Our findings are consistent with a specific role for C4A protein in schizophrenia and raise the possibility that its activation product, C4-ana, increases BBB permeability. Exploratory analyses suggest the novel hypothesis that the relationship between C4-ana levels and C4A gene copy number could also be altered in iSCZ, suggesting an interaction with unknown genetic and/or environmental risk factors.

Levels of lymphocyte-associated regulators of complement system CD55 and CD59 are changed in schizophrenia patients

OBJECTIVE

Although pathological mechanisms of schizophrenia are unknown, evidence in the literature suggests that the immune system might be involved in the pathogenesis. Complement is an important part of the immune system and it has been suggested to play role in the pathogenesis of schizophrenia. We aimed to investigate the potential involvement of the complement system in schizophrenia by the determination of peripheral concentrations of certain complement proteins and their regulators in patients.

METHODS

Plasma concentrations of complement C3, C4, and C1 inhibitory protein were measured by chemiluminescence in 41 schizophrenia patients and 39 healthy controls. Expression of CD55, CD59, and CD46 proteins on peripheral blood mononuclear cells were determined by flow cytometry in the same groups.

RESULTS

Frequencies of peripheral immune cells expressing CD55 were determined to be significantly higher in schizophrenia patients than in healthy people (p = 0.020). Frequencies of peripheral immune cells expressing CD59 was determined to be significantly higher in healthy people than in schizophrenia patients (p = 0.012). The expression level of CD55 per cell was measured to be significantly elevated in patients compared to healthy controls (p = 0.026).

CONCLUSIONS

Our data clearly demonstrate an elevated complement activity in schizophrenia and points to a possible complement association in the pathogenesis.Key pointsIncreased the expression level, and frequency of CD55 in schizophrenia patients.Decreased frequency of CD59 in schizophrenia patients.No difference in the expression level of CD59; the expression level, and frequency of CD46; frequency of complement C3, C4, and C1 inhibitory protein.

Complement C4 associations with altered microbial biomarkers exemplify gene-by-environment interactions in schizophrenia

Schizophrenia is a complex brain disorder with genetic and environmental factors contributing to its etiology. Complement C4 genes are schizophrenia susceptibility loci and are activated in response to infections and gut microbiome imbalances. We hypothesize that C4 genetic susceptibility predisposes individuals to neuropathological effects from pathogen exposures or a microbiome in dysbiosis. In 214 individuals with schizophrenia and 123 non-psychiatric controls, we examined C4 gene copy number and haplotype groups for associations with schizophrenia and microbial plasma biomarkers. C4A copy number and haplotypes containing HERV-K insertions (C4A-long; C4AL-C4AL) conferred elevated odds ratios for schizophrenia diagnoses (OR 1.58-2.56, p < 0.0001), while C4B-short (C4BS) haplogroups conferred decreased odds (OR 0.43, p < 0.0001). Haplogroup-microbe combinations showed extensive associations with schizophrenia including C4AL with Candida albicans IgG (OR 2.16, p < 0.0005), C4AL-C4BL with cytomegalovirus (CMV) IgG (OR 1.79, p < 0.008), C4BS with lipopolysaccharide-binding protein (LBP) (OR 1.18, p < 0.0001), and C4AL-C4AL with Toxoplasma gondii IgG (OR = 17.67, p < 0.0001). In controls, only one haplogroup-microbe combination was significant: C4BS with CMV IgG (OR 0.52, p < 0.02). In schizophrenia only, LBP and CMV IgG levels were inversely correlated with C4A and C4S copy numbers, respectively (R2 = 0.13-0.16, p < 0.0001). C4 haplogroups were associated with altered scores of cognitive functioning in both cases and controls and with psychiatric symptom scores in schizophrenia. Our findings link complement C4 genes with a susceptibility to infections and a dysbiotic microbiome in schizophrenia. These results support immune system mechanisms by which gene-environmental interactions may be operative in schizophrenia.

Aberrant Complement System Activation in Neurological Disorders

The complement system is an assembly of proteins that collectively participate in the functions of the healthy and diseased brain. The complement system plays an important role in the maintenance of uninjured (healthy) brain homeostasis, contributing to the clearance of invading pathogens and apoptotic cells, and limiting the inflammatory immune response. However, overactivation or underregulation of the entire complement cascade within the brain may lead to neuronal damage and disturbances in brain function. During the last decade, there has been a growing interest in the role that this cascading pathway plays in the neuropathology of a diverse array of brain disorders (e.g., acute neurotraumatic insult, chronic neurodegenerative diseases, and psychiatric disturbances) in which interruption of neuronal homeostasis triggers complement activation. Dysfunction of the complement promotes a disease-specific response that may have either beneficial or detrimental effects. Despite recent advances, the explicit link between complement component regulation and brain disorders remains unclear. Therefore, a comprehensible understanding of such relationships at different stages of diseases could provide new insight into potential therapeutic targets to ameliorate or slow progression of currently intractable disorders in the nervous system. Hence, the aim of this review is to provide a summary of the literature on the emerging role of the complement system in certain brain disorders.

Peripheral immune markers and antipsychotic non-response in psychosis

BACKGROUND

Peripheral immune markers have previously been linked to a poor response to antipsychotic medication and more severe negative symptoms at the onset of psychosis. The present study investigated the association of blood cytokines and complement markers with the presence of antipsychotic non-response and symptom severity in patients with psychosis.

METHODS

This cross-sectional study recruited 94 patients with schizophrenia and other psychoses, of whom 47 were defined as antipsychotic responders and 47 as antipsychotic non-responders. In all subjects we measured plasma levels of cytokines (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, TNF-α, and IFN-γ), complement markers (C1-inhibitor, C3, C4, C3a, C3b, Bb, factor D, C5a, terminal complement complex) and high sensitivity C-reactive protein (hsCRP). Symptom severity was recorded using the Positive and Negative Syndrome scale for Schizophrenia (PANSS). Binary logistic regression tested each immune marker as predictor of response status while covarying for relevant socio-demographic variables. Correlation analyses tested the association between immune markers and the severity of symptoms.

RESULTS

Interleukin (IL)-8 significantly predicted antipsychotic non-response (OR=24.70, 95% CI, 1.35-453.23, p = 0.03). Other immune markers were not associated with antipsychotic response. IL-6, IL-8, IL-10 and TNF-α significantly positively correlated with negative psychotic symptoms.

CONCLUSIONS

Higher levels of IL-8 are associated with a poor response to antipsychotic treatment. Increased cytokines levels are specifically associated with more severe negative symptoms in patients with schizophrenia and other psychoses.

Association between complement component 4A expression, cognitive performance and brain imaging measures in UK Biobank

Abstract.

BACKGROUND

Altered expression of the complement component C4A gene is a known risk factor for schizophrenia. Further, predicted brain C4A expression has also been associated with memory function highlighting that altered C4A expression in the brain may be relevant for cognitive and behavioral traits.

METHODS

We obtained genetic information and performance measures on seven cognitive tasks for up to 329 773 individuals from the UK Biobank, as well as brain imaging data for a subset of 33 003 participants. Direct genotypes for variants (n = 3213) within the major histocompatibility complex region were used to impute C4 structural variation, from which predicted expression of the C4A and C4B genes in human brain tissue were predicted. We investigated if predicted brain C4A or C4B expression were associated with cognitive performance and brain imaging measures using linear regression analyses.

RESULTS

We identified significant negative associations between predicted C4A expression and performance on select cognitive tests, and significant associations with MRI-based cortical thickness and surface area in select regions. Finally, we observed significant inconsistent partial mediation of the effects of predicted C4A expression on cognitive performance, by specific brain structure measures.

CONCLUSIONS

These results demonstrate that the C4 risk locus is associated with the central endophenotypes of cognitive performance and brain morphology, even when considered independently of other genetic risk factors and in individuals without mental or neurological disorders.

Complement pathway changes at age 12 are associated with psychotic experiences at age 18 in a longitudinal population-based study: evidence for a role of stress

The complement cascade is a major component of the immune defence against infection, and there is increasing evidence for a role of dysregulated complement in major psychiatric disorders. We undertook a directed proteomic analysis of the complement signalling pathway (n = 29 proteins) using data-independent acquisition. Participants were recruited from the UK avon longitudinal study of parents and children (ALSPAC) cohort who participated in psychiatric assessment interviews at ages 12 and 18. Protein expression levels at age 12 among individuals who reported psychotic experiences (PEs) at age 18 (n = 64) were compared with age-matched controls (n = 67). Six out of the 29 targeted complement proteins or protein subcomponents were significantly upregulated following correction for multiple comparisons (VTN↑, C1RL↑, C8B↑, C8A↑, CFH↑, and C5↑). We then undertook an unbiased plasma proteomic analysis of mice exposed to chronic social stress and observed dysregulation of 11 complement proteins, including three that were altered in the same direction in individuals with PE (C1R↑, CFH↑, and C5↑). Our findings indicate that dysregulation of the complement protein pathway in blood is associated with incidence of psychotic experiences and that these changes may reflect exposure to stress.

Higher Serum C-Reactive Protein Levels in Catatonic Patients: A Comparison to Non-catatonic Patients and Healthy Controls

Catatonia is a psychomotor syndrome defined by a constellation of predominantly motor symptoms. The aim of the present study was to determine whether recently admitted psychiatric patients with catatonia exhibited higher serum C-reactive protein (hs-CRP) levels compared to non-catatonic psychiatric patients and healthy controls (HCs). Recently admitted psychiatric patients were screened and evaluated for the catatonia syndrome using the Bush-Francis Catatonia Rating Scale and the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). The study sample was formed by 150 individuals (39 male and 111 female), including 51 catatonic patients, 55 non-catatonic patients, and 44 HCs. Serum hs-CRP levels were processed with the enzyme-linked immunosorbent assay. Serum levels of creatine kinase (CK), adrenocorticotropic hormone (ACTH), immunoglobulin G (IgG), complement component 3 (C3), and complement component 4 (C4) were also determined. There was a significantly higher percentage of patients with high inflammatory levels (hs-CRP > 3000ng/ml) in the catatonic (43.1%) than in the non-catatonic (14.5%) or HCs group (9.1%) (χ 2 =18.9, P < .001). Logistic regression showed that catatonic patients had significantly higher hs-CRP levels compared to non-catatonic patients even after controlling for other clinical and laboratory variables (OR = 3.52, P = .015, 95% CI 1.28-9.79). Multiple linear regression analysis revealed that log-transformed hs-CRP was independently predicted by body mass index and log-transformed C4, ACTH, and Cortisol in catatonic patients. Findings of the present study suggest that catatonia is specifically linked to a higher level of systemic inflammation, not merely attributable to the overall psychopathology, or alterations in the stress level and complement system.

Positive association between PTN polymorphisms and schizophrenia in Northeast Chinese Han population

As a severely and highly heritable psychotic disorder, schizophrenia has become a serious public health problem in modern society. Pleiotrophin (PTN) is a secreted cell cytokine associated with the extracellular matrix and acts as a growth factor. PTN is mainly expressed in neuroectodermal and mesodermal tissues, indicating its effect in neuron migration and epithelium-mesenchyme interactions. Whereas PTN is associated with some neurodegenerative diseases and has modulating effects on them. In this study, we aimed to investigate the association between PTN polymorphisms and schizophrenia in an independent case-control sample-set including 738 schizophrenia patients and 1085 healthy controls. Of the 13 selected single nucleotide polymorphisms (SNPs), five showed significant differences in allele or/and genotype frequencies between patients and controls: rs3959914 (genotype: χ = 11.5217, P = 0.0032); rs11765480 (genotype: χ = 10.6620, P = 0.0049); rs1473355 (genotype: χ = 8.3902, P = 0.0151); rs322246 (allele: χ = 5.5954, P = 0.0180); rs322240 (genotype: χ = 8.8429, P = 0.0121; allele: χ = 8.7802, P = 0.0031). The haplotype analysis of the selected SNPs showed different haplotype frequencies for one block (rs322240, rs322246) between cases and controls (global: χ = 9.0290, P = 0.0110; A-G: χ = 8.985, P = 0.0027; C-A: χ = 5.814, P = 0.0159). Our present results indicate PTN as a susceptibility gene for schizophrenia.

Peripheral complement proteins in schizophrenia: A systematic review and meta-analysis of serological studies

BACKGROUND

There is renewed focus on the complement system in the pathogenesis of schizophrenia. In addition to providing aetiological insights, consistently dysregulated complement proteins in serum or plasma may have clinical utility as biomarkers.

METHODS

We performed a systematic literature review searching PubMed, Embase and PsycINFO for studies measuring complement system activity or complement protein concentrations in serum or plasma from patients with schizophrenia compared to controls. Random-effects meta-analyses were performed to calculate pooled effect estimates (Hedges' g standardised mean difference [SMD]) for complement proteins whose concentrations were measured in three or more studies. The review was pre-registered on the PROSPERO database (CRD42018109012).

RESULTS

Database searching identified 1146 records. Fifty-eight full-text articles were assessed for eligibility and 24 studies included. Seven studies measured complement system activity. Activity of the classical pathway did not differ between cases and controls in four of six studies, and conflicting results were noted in two studies of alternative pathway activity. Twenty studies quantified complement protein concentrations of which complement components 3 (C3) and 4 (C4) were measured in more than three studies. Meta-analyses showed no evidence of significant differences between cases and controls for 11 studies of C3 (SMD 0.04, 95% confidence interval [CI] -0.29-0.36) and 10 studies of C4 (SMD 0.10, 95% CI -0.21-0.41).

CONCLUSIONS

Serological studies provide mixed evidence regarding dysregulation of the complement system in schizophrenia. Larger studies of a longitudinal nature, focusing on early phenotypes, could provide further insights regarding the potential role of the complement system in psychotic disorders.

Inflammatory Pathways in Psychiatric Disorders: The case of Schizophrenia and Depression

Purpose of Review

A better understanding of the key molecules/pathways underlying the pathophysiology of depression and schizophrenia may contribute to novel therapeutic strategies. In this review, we have discussed the recent developments on the role of inflammatory pathways in the pathogenesis of depression and schizophrenia.

Recent Findings

Inflammation is an innate immune response that can be triggered by various factors, including pathogens, stress and injury. Under normal conditions, the inflammatory responses quiet after pathogen clearance and tissue repair. However, abnormal long-term or chronic inflammation can lead to damaging effects. Accumulating evidence suggest that dysregulated inflammation is linked to the pathogenesis of neuropsychiatric disorders. In this review, we have discussed the roles of complement system, infiltration of peripheral immune cells into the central nervous system (CNS), the gut-brain axis, and the kynurenine pathway in depression and schizophrenia.

Summary

There is a large body of compelling evidence on the role of inflammatory pathways in depression and schizophrenia. Although most of these findings show their roles in the pathophysiology of the above disorders, additional studies are warranted to investigate the therapeutic potential of various immune signaling targets discussed in this article.

Association of the CACNA2D2 gene with schizophrenia in Chinese Han population

Background

Schizophrenia (SCZ) is a severely complex psychiatric disorder in which ~80% can be explained by genetic factors. Single nucleotide polymorphisms (SNPs) in calcium channel genes are potential genetic risk factors for a spectrum of psychiatric disorders including SCZ. This study evaluated the association between SNPs in the voltage-gated calcium channel auxiliary subunit alpha2delta 2 gene (CACNA2D2) and SCZ in the Han Chinese population of Northeast China.

Methods

A total of 761 SCZ patients and 775 healthy controls were involved in this case-control study. Three SNPs (rs3806706, rs45536634 and rs12496815) of CACNA2D2 were genotyped by the MALDI-TOF-MS technology. Genotype distribution and allele frequency differences between cases and controls were tested by Chi-square (χ²) in males and females respectively using SPSS 24.0 software. Linkage disequilibrium and haplotype analyses were conducted using Haploview4.2. The false discovery rate correction was utilized to control for Type I error by R3.2.3.

Results

There was a significant difference in allele frequencies (χ² = 9.545, P_adj = 0.006) and genotype distributions (χ² = 9.275, P_adj = 0.006) of rs45536634 between female SCZ patients and female healthy controls after adjusting for multiple comparisons. Minor allele A (OR = 1.871, 95% CI [1.251–2.798]) and genotype GA + AA (OR = 1.931, 95% CI [1.259–2.963]) were associated with an increased risk of SCZ. Subjects with haplotype AG consisting of rs45536634 and rs12496815 alleles had a higher risk of SCZ (OR = 1.91, 95% CI [1.26–2.90]) compared those with other haplotypes.

Conclusions

This study provides evidence that CACNA2D2 polymorphisms may influence the susceptibility to SCZ in Han Chinese women.

The complement system in schizophrenia: where are we now and what's next?

The complement system is a set of immune proteins involved in first-line defense against pathogens and removal of waste materials. Recent evidence has implicated the complement cascade in diseases involving the central nervous system, including schizophrenia. Here, we provide an up-to-date narrative review and critique of the literature on the relationship between schizophrenia and complement gene polymorphisms, gene expression, protein concentration, and pathway activity. A literature search identified 23 new studies since the first review on this topic in 2008. Overall complement pathway activity appears to be elevated in schizophrenia. Recent studies have identified complement component 4 (C4) and CUB and Sushi Multiple Domains 1 (CSMD1) as potential genetic markers of schizophrenia. In particular, there is some evidence of higher rates of C4B/C4S deficiency, reduced peripheral C4B concentration, and elevated brain C4A mRNA expression in schizophrenia patients compared to controls. To better elucidate the additive effects of multiple complement genotypes, we also conducted gene- and gene-set analysis through MAGMA which supported the role of Human Leukocyte Antigen class (HLA) III genes and, to a lesser extent, CSMD1 in schizophrenia; however, the HLA-schizophrenia association was likely driven by the C4 gene. Lastly, we identified several limitations of the literature on the complement system and schizophrenia, including: small sample sizes, inconsistent methodologies, limited measurements of neural concentrations of complement proteins, little exploration of the link between complement and schizophrenia phenotype, and lack of studies exploring schizophrenia treatment response. Overall, recent findings highlight complement components-in particular, C4 and CSMD1-as potential novel drug targets in schizophrenia. Given the growing availability of complement-targeted therapies, future clinical studies evaluating their efficacy in schizophrenia hold the potential to accelerate treatment advances.

Evaluation of miRNA Expression Profiles in Schizophrenia Using Principal-Component Analysis-Based Unsupervised Feature Extraction Method

Schizophrenia (SZ) is a disease that causes mental disability and affects 1% of the total population in the world. Our aim was to identify new molecular targets that would help to diagnose and treat these patients. The GSE54578 microRNA expression profile was downloaded from the Gene Expression Omnibus database that consists of peripheral blood samples of 15 first-onset SZ patients and 15 healthy controls. Principal-component analysis-based unsupervised feature extraction (FE), protein-protein interaction network, and pathway enrichment were performed, and microRNA (miRNA)-hub gene network was established. A set of seven miRNA (hsa-miR-373-5p, hsa-miR-199a-3p, hsa-miR-22-5p, hsa-miR-4711-3p, hsa-miR-3157-3p, hsa-miR-542-5p, and hsa-miR-3615) could successfully discriminate SZ patients from healthy controls with high accuracy. We identified two miRNAs (hsa-miR-373-5p and hsa-miR-199a-3p) as a signature that mostly related to SZ. These miRNAs could be potential novel biomarkers and could contribute to the clinical treatment of this disease.

Microglial cell hyper-ramification and neuronal dendritic spine loss in the hippocampus and medial prefrontal cortex in a mouse model of PTSD

Few animal models exist that successfully reproduce several core associative and non-associative behaviours relevant to post-traumatic stress disorder (PTSD), such as long-lasting fear reactions, hyperarousal, and subtle attentional and cognitive dysfunction. As such, these models may lack the face validity required to adequately model pathophysiological features of PTSD such as CNS grey matter loss and neuroinflammation. Here we aimed to investigate in a mouse model of PTSD whether contextual fear conditioning associated with a relatively high intensity footshock exposure induces loss of neuronal dendritic spines in various corticolimbic brain regions, as their regression may help explain grey matter reductions in PTSD patients. Further, we aimed to observe whether these changes were accompanied by alterations in microglial cell number and morphology, and increased expression of complement factors implicated in the mediation of microglial cell-mediated engulfment of dendritic spines. Adult male C57Bl6J mice were exposed to a single electric footshock and subsequently underwent phenotyping of various PTSD-relevant behaviours in the short (day 2-4) and longer-term (day 29-31). 32 days post-exposure the brains of these animals were subjected to Golgi staining of dendritic spines, microglial cell Iba-1 immunohistochemistry and immunofluorescent staining of the complement factors C1q and C4. Shock exposure promoted a lasting contextual fear response, decreased locomotor activity, exaggerated acoustic startle responses indicative of hyperarousal, and a short-term facilitation of sensorimotor gating function. The shock triggered loss of dendritic spines on pyramidal neurons was accompanied by increased microglial cell number and complexity in the medial prefrontal cortex and dorsal hippocampus, but not in the amygdala. Shock also increased expression of C1q in the pyramidal layer of the CA1 region of the hippocampus but not in other brain regions. The present study further elaborates on the face and construct validity of a mouse model of PTSD and provides a good foundation to explore potential molecular interactions between microglia and dendritic spines.

Identification of serum microRNAs as diagnostic biomarkers for schizophrenia

Background

At present, the schizophrenia diagnoses are based on the clinical symptoms and behaviors neglecting the laboratory test indicators.

Results

To better investigate the diagnostic potential of miRNAs for schizophrenia, we selected 14 candidate miRNAs and examined their expressions in the serums of 40 schizophrenia patients and 40 healthy controls by qRT-PCR. Ultimately three abnormally expressed microRNAs were identified, i.e., miR-34a-5p, miR-432-5p and miR-449a. Then, binary regression analysis was employed to combine 3 dysregulated miRNAs. ROC analysis revealed that the AUC of the combination of miR-432-5p + miR-449a in serums was 0.841 (95% CI: 0.791~0.887) with 90% sensitivity and 80% specificity. The AUC of the combination of miR-34a-5p + miR-432-5p + miR-449a in serums was 0.843 (95% CI: 0.791~0.887) with 90% sensitivity and 77.5% specificity. The results indicated that the combined model of miR-432-5p + miR-449a and miR-34a-5p + miR-432-5p + miR-449a have better prediction performances.

Conclusions

The study concludes that the two miRNAs combinations have the potential to be used as biomarkers for schizophrenia diagnoses. The finding may be conducive to overcoming the dilemmas faced by current schizophrenia diagnosis.

Complement system biomarkers in first episode psychosis

Several lines of evidence implicate immunological/inflammatory factors in development of schizophrenia. Complement is a key driver of inflammation, and complement dysregulation causes pathology in many diseases. Here we explored whether complement dysregulation occurred in first episode psychosis (FEP) and whether this provides a source of biomarkers. Eleven complement analytes (C1q, C3, C4, C5, factor B [FB], terminal complement complex [TCC], factor H [FH], FH-related proteins [FHR125], Properdin, C1 inhibitor [C1inh], soluble complement receptor 1 [CR1]) plus C-reactive protein (CRP) were measured in serum from 136 first episode psychosis (FEP) cases and 42 mentally healthy controls using established in-house or commercial ELISA. The relationship between caseness and variables (analytes measured, sex, age, ethnicity, tobacco/cannabis smoking) was tested by multivariate logistic regression. When measured individually, only TCC was significantly different between FEP and controls (p=0.01). Stepwise selection demonstrated interdependence between some variables and revealed other variables that significantly and independently contributed to distinguishing cases and controls. The final model included demographics (sex, ethnicity, age, tobacco smoking) and a subset of analytes (C3, C4, C5, TCC, C1inh, FHR125, CR1). A receiver operating curve analysis combining these variables yielded an area under the curve of 0.79 for differentiating FEP from controls. This model was confirmed by multiple replications using randomly selected sample subsets. The data suggest that complement dysregulation occurs in FEP, supporting an underlying immune/inflammatory component to the disorder. Classification of FEP cases according to biological variables rather than symptoms would help stratify cases to identify those that might most benefit from therapeutic modification of the inflammatory response.

Associations Between Non-neurological Autoimmune Disorders and Psychosis: A Meta-analysis

BACKGROUND

A relationship between non-neurological autoimmune (NNAI) disorders and psychosis has been widely reported but not yet subjected to meta-analysis. We conducted the first meta-analysis examining the association between NNAI disorders and psychosis and investigated the effect of 1) temporality (as determined by study design), 2) psychiatric diagnosis, and 3) specific autoimmune disorders.

METHODS

Major databases were searched for articles published until April 2018; 31 studies, comprising data for >25 million individuals, were eligible. Using random-effects models, we examined the overall association between all NNAI disorders and psychosis; rheumatoid arthritis was examined separately given the well-established negative association with psychosis. Stratified analyses investigated the effect of temporality, psychiatric diagnosis, and specific NNAI disorders.

RESULTS

We observed a positive overall association between NNAI disorders and psychosis (odds ratio [OR] = 1.26; 95% confidence interval [CI], 1.12-1.41) that was consistent across study designs and psychiatric diagnoses; however, considerable heterogeneity was detected (I² = 88.08). Patterns varied across individual NNAI disorders; associations were positive for pernicious anemia (OR = 1.91; 95% CI, 1.29-2.84), pemphigoid (OR = 1.90; 95% CI, 1.62-2.24), psoriasis (OR = 1.70; 95% CI, 1.51-1.91), celiac disease (OR = 1.53; 95% CI, 1.12-2.10), and Graves' disease (OR = 1.33; 95% CI, 1.03-1.72) and negative for ankylosing spondylitis (OR = 0.72; 95% CI, 0.54-0.98) and rheumatoid arthritis (OR = 0.65; 95% CI, 0.50-0.84).

CONCLUSIONS

While we observed a positive overall association between NNAI disorders and psychosis, this was not consistent across all NNAI disorders. Specific factors, including distinct inflammatory pathways, genetic influences, autoantibodies targeting brain proteins, and exposure to corticosteroid treatment, may therefore underlie this association.

Basic Concept of Microglia Biology and Neuroinflammation in Relation to Psychiatry

The hypothesis that the neuroimmune system plays a role in the pathogenesis of different psychiatric disorders, including schizophrenia, depression, and bipolar disease, has attained increasing interest over the past years. Previously thought to have the sole purpose of protecting the central nervous system (CNS) from harmful stimuli, it is now known that the central immune system is critically involved in regulating physiological processes including neurodevelopment, synaptic plasticity, and circuit maintenance. Hence, alterations in microglia - the main immune cell of the CNS - and/or inflammatory factors do not unequivocally connote ongoing neuroinflammation or neuroinflammatory processes per se but rather might signify changes in brain homoeostasis. Despite this, psychiatric research tends to equate functional changes in microglia or alterations in other immune mediators with neuroinflammation. It is the main impetus of this chapter to overcome some of the current misconceptions and possible oversimplifications with respect to neuroinflammation and microglia activity in psychiatry. In order to do so, we will first provide an overview of the basic concepts of neuroinflammation and neuroinflammatory processes. We will then focus on microglia with respect to their ontogeny and immunological and non-immunological functions presenting novel insights on how microglia communicate with other cell types of the central nervous system to ensure proper brain functioning. And lastly, we will delineate the non-immunological functions of inflammatory cytokines in order to address the possible misconception of equating alterations in central cytokine levels with ongoing central inflammation. We hereby hope to help unravel the functional relevance of neuroimmune dysfunctions in psychiatric illnesses and provide future research directions in the field of psychoneuroimmunology.

Emerging Roles of Complement in Psychiatric Disorders

The complement system consists of more than 30 proteins that have long been known to participate to the immune defence against pathogens and to the removal of damaged cells. Their role, however, extends beyond immunity and clearance of altered "self" components in the periphery. In particular, complement proteins can be induced by all cell types in the brain. Recent discoveries highlight the role of complement in normal and pathological brain development. Specifically, the complement system mediates synaptic pruning, a developmental process whereby supernumerary synapses are eliminated in the immature brain. The complement system has been implicated in pathological synapse elimination in schizophrenia, West Nile virus infection, and lupus, all of which are associated with psychiatric manifestations. Complement also contributes to synapse loss in neurodegenerative conditions. This review provides a brief overview of the well-studied role of complement molecules in immunity. The contribution of complement to embryonic and adult neurogenesis, neuronal migration, and developmental synaptic elimination in the normal brain is reviewed. We discuss the role of complement in synapse loss in psychiatric and neurological diseases and evaluate the therapeutic potential of complement-targeting drugs for brain disorders.

Mass spectrometry identification of potential biomarker proteins in the 150-kD electrophoretic band in patients with schizophrenia

BACKGROUND

Diagnosing schizophrenia is primarily based on the presentation of defined signs and symptoms, none of which is pathognomonic for this group of syndromes. However, few significant genome-wide associations between schizophrenia and individual have detected. Protein profiling of candidate serum biomarkers in schizophrenia is therefore an area of great interest.

METHODS

In the present study, we used a combination of 7% polyethylene glycol (PEG) enrichment of immune complexes and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to separate abnormal band, then analyse the band with liquid chromatography mass spectrometry (LC-MS).

RESULTS

There is a special 150-kD electrophoretic band in patients with schizophrenia, bipolar disorder, or depression relative to healthy controls (each 30 samples). Analysis of the band using LC-MS resulted in the identification of 11 serum proteins whose abundance was altered between patients and controls. Among them, 8 proteins (CFH, CFB, cDNA FLJ75416, zinc finger protein 729, isoform 2 of nidogen-1, diaphanous-1, cDNA FLJ77762, and cDNA FLJ58411) were up regulated, while one protein (isoform 1 of collagen alpha-1 (II) was down regulated in patients with schizophrenia, but only zinc finger protein 729 has statistics significance (P < .05). No differences were noted with regard to thrombospondin-1 or collagen alpha-2 (I) among the 3 groups. These proteins take part in several biological functions such as focal adhesion, complement cascades, ECM-receptor interaction, and Staphylococcus aureus infection.

CONCLUSIONS

The 150-kD electrophoretic band or zinc finger protein 729 may become biomarkers in patients with schizophrenia. In the future increasing sample size and function research of zinc finger protein 729 should be executed continuously.

Autoimmune phenotypes in schizophrenia reveal novel treatment targets

Typical and atypical antipsychotics are the first-line treatments for schizophrenia, but these classes of drugs are not universally effective, and they can have serious side effects that impact compliance. Antipsychotic drugs generally target the dopamine pathways with some variation. As research of schizophrenia pathophysiology has shifted away from a strictly dopamine-centric focus, the development of new pharmacotherapies has waned. A field of inquiry with centuries-old roots is gaining traction in psychiatric research circles and may represent a new frontier for drug discovery in schizophrenia. At the forefront of this investigative effort is the immune system and its many components, pathways and phenotypes, which are now known to actively engage the brain. Studies in schizophrenia reveal an intricate association of environmentally-driven immune activation in concert with a disrupted genetic template. A consistent conduit through this gene-environmental milieu is the gut-brain axis, which when dysregulated can generate pathological autoimmunity. In this review, we present epidemiological and biochemical evidence in support of an autoimmune component in schizophrenia and depict gut processes and a dysbiotic microbiome as a source and perpetuator of autoimmune dysfunction in the brain. Within this framework, we review the role of infectious agents, inflammation, gut dysbioses and autoantibody propagation on CNS pathologies such as neurotransmitter receptor hypofunction and complement pathway-mediated synaptic pruning. We then review the new pharmacotherapeutic horizon and novel agents directed to impact these pathological conditions. At the core of this discourse is the understanding that schizophrenia is etiologically and pathophysiologically heterogeneous and thus its treatment requires individualized attention with disease state variants diagnosed with objective biomarkers.

Be on Target: Strategies of Targeting Alternative and Lectin Pathway Components in Complement-Mediated Diseases

The complement system has moved into the focus of drug development efforts in the last decade, since its inappropriate or uncontrolled activation has been recognized in many diseases. Some of them are primarily complement-mediated rare diseases, such as paroxysmal nocturnal hemoglobinuria, C3 glomerulonephritis, and atypical hemolytic uremic syndrome. Complement also plays a role in various multifactorial diseases that affect millions of people worldwide, such as ischemia reperfusion injury (myocardial infarction, stroke), age-related macular degeneration, and several neurodegenerative disorders. In this review, we summarize the potential advantages of targeting various complement proteins with special emphasis on the components of the lectin (LP) and the alternative pathways (AP). The serine proteases (MASP-1/2/3, factor D, factor B), which are responsible for the activation of the cascade, are straightforward targets of inhibition, but the pattern recognition molecules (mannose-binding lectin, other collectins, and ficolins), the regulatory components (factor H, factor I, properdin), and C3 are also subjects of drug development. Recent discoveries about cross-talks between the LP and AP offer new approaches for clinical intervention. Mannan-binding lectin-associated serine proteases (MASPs) are not just responsible for LP activation, but they are also indispensable for efficient AP activation. Activated MASP-3 has recently been shown to be the enzyme that continuously supplies factor D (FD) for the AP by cleaving pro-factor D (pro-FD). In this aspect, MASP-3 emerges as a novel feasible target for the regulation of AP activity. MASP-1 was shown to be required for AP activity on various surfaces, first of all on LPS of Gram-negative bacteria.

Prenatal inflammation and risk for schizophrenia: A role for immune proteins in neurodevelopment

Prenatal inflammation is an established risk factor for schizophrenia. However, the specific inflammatory pathways that mediate this association remain unclear. Potential candidate systems include inflammatory markers produced by microglia, such as cytokines and complement. Accumulating evidence suggests that these markers play a role in typical neurodevelopmental processes, such as synapse formation and interneuron migration. Rodent models demonstrate that altered marker levels during the prenatal period can cause lasting deficits in these systems, leading to cognitive deficits that resemble schizophrenia. This review assesses the potential role of prenatal cytokine and complement elevations on the etiology of schizophrenia. The current neurobiological understanding of the development of schizophrenia is reviewed to identify candidate cellular mechanisms that may be influenced by prenatal inflammation. We discuss the functions that cytokines and complement may play in prenatal neurodevelopment, review evidence that links exposure to these factors with risk for schizophrenia, and consider how these markers may interact with genetic vulnerabilities to influence the neurodevelopment of schizophrenia. We consider how prenatal inflammatory exposure may influence childhood and adolescent developmental risk trajectories for schizophrenia. Finally, we identify areas of further research needed to support the development of anti-inflammatory treatments to prevent the development of schizophrenia in at-risk neonates.

Neuropil contraction in relation to Complement C4 gene copy numbers in independent cohorts of adolescent-onset and young adult-onset schizophrenia patients-a pilot study

A recent report suggested Complement 4 (C4A) gene copy numbers (GCN) as risk factors for schizophrenia. Rodent model showed association of C4 with synaptic pruning suggesting its pathophysiological significance (Sekar, A. et al. (2016)). We, therefore, predicted that C4A GCN would be positively correlated with neuropil contraction in the human brain among schizophrenia patients showing more prominent correlations in ventral regions among young adults and dorsal regions among adolescents since neuromaturation progresses dorsoventrally. Whole-brain, multi-voxel, in vivo phosphorus magnetic resonance spectroscopy (³¹P MRS) assessed neuropil changes by estimating levels of membrane phospholipid (MPL) precursors and catabolites. Increased MPL catabolites and/or decreased MPL precursors indexed neuropil contraction. Digital droplet PCR-based assay was used to estimate C4A and C4B GCN. We evaluated two independent cohorts (young adult-onset early-course schizophrenia (YASZ = 15) and adolescent-onset schizophrenia (AOSZ = 12) patients), and controls matched for each group, n = 22 and 15, respectively. Separate forward stepwise linear regression models with Akaike information Criterion were built for MPL catabolites and precursors. YASZ cohort: Consistent with the rodent model (Sekar, A. et al. 2016)), C4A GCN positively correlated with neuropil contraction (increased pruning/decreased formation) in the inferior frontal cortex and inferior parietal lobule. AOSZ cohort: C4A GCN positively correlated with neuropil contraction in the dorsolateral prefrontal cortex and thalamus. Exploratory analysis of C4B GCN showed positive correlation with neuropil contraction in the cerebellum and superior temporal gyrus among YASZ while AOSZ showed neuropil contraction in the prefrontal and subcortical structures. Thus, C4A and C4B GCN are associated with neuropil contraction in regions often associated with schizophrenia, and may be neuromaturationally dependent.

C4A mRNA expression in PBMCs predicts the presence and severity of delusions in schizophrenia and bipolar disorder with psychosis

Altered immune function is an established finding in psychotic disorders such as schizophrenia and bipolar disorder with psychosis, though its role in their development and progression remains to be understood. Evidence suggests altered JAK-STAT1 pathway activity in peripheral blood cells from participants with schizophrenia compared to controls. Activation of this pathway leads to increased expression of complement component 4A (C4A), which has recently been implicated in schizophrenia. Here, we examine mRNA expression of C4A in peripheral blood cells from participants with schizophrenia, bipolar disorder and controls. STAT1 and IRF-1 mRNA expression are included as measures of JAK-STAT1 pathway activation in the same participants. Further, we examine the association of each genes mRNA expression with clinical symptom measures using the Positive and Negative Syndrome Scale (PANSS) and the Psychotic Symptom Rating Scale (PSYRATS). We demonstrate that C4A, STAT1 and IRF-1 mRNA expression levels are correlated across the entire sample, indicating shared transcriptional regulatory mechanisms. Further, we show that C4A mRNA expression alone is positively associated with psychotic symptomatology, specifically the presence and severity of delusions. These findings are noteworthy given recent findings that demonstrate a critical role for complement proteins in synaptic pruning, alterations of which are proposed to contribute to psychopathology in psychosis.

Recent Advances in the Genetics of Schizophrenia

The last decade brought tremendous progress in the field of schizophrenia genetics. As a result of extensive collaborations and multiple technological advances, we now recognize many types of genetic variants that increase the risk. These include large copy number variants, rare coding inherited and de novο variants, and over 100 loci harboring common risk variants. While the type and contribution to the risk vary among genetic variants, there is concordance in the functions of genes they implicate, such as those whose RNA binds the fragile X-related protein FMRP and members of the activity-regulated cytoskeletal complex involved in learning and memory. Gene expression studies add important information on the biology of the disease and recapitulate the same functional gene groups. Studies of alternative phenotypes help us widen our understanding of the genetic architecture of mental function and dysfunction, how diseases overlap not only with each other but also with non-disease phenotypes. The challenge is to apply this new knowledge to prevention and treatment and help patients. The data generated so far and emerging technologies, including new methods in cell engineering, offer significant promise that in the next decade we will unlock the translational potential of these significant discoveries.

HLA typing using genome wide data reveals susceptibility types for infections in a psychiatric disease enriched sample

BACKGROUND

The infections Toxoplasma gondii (T. gondii), cytomegalovirus, and Herpes Simplex Virus Type 1 (HSV1) are common persistent infections that have been associated with schizophrenia and bipolar disorder. The major histocompatibility complex (MHC, termed HLA in humans) region has been implicated in these infections and these mental illnesses. The interplay of MHC genetics, mental illness, and infection has not been systematically examined in previous research.

METHODS

In a cohort of 1636 individuals, we used genome-wide association data to impute 7 HLA types (A, B, C, DRB1, DQA1, DQB1, DPB1), and combined this data with serology data for these infections. We used regression analysis to assess the association between HLA alleles, infections (individually and collectively), and mental disorder status (schizophrenia, bipolar disorder, controls).

RESULTS

After Bonferroni correction for multiple comparisons, HLA C∗07:01 was associated with increased HSV1 infection among mentally healthy controls (OR 3.4, p = 0.0007) but not in the schizophrenia or bipolar groups (P > 0.05). For the multiple infection outcome, HLA B∗ 38:01 and HLA C∗12:03 were protective in the healthy controls (OR ≈ 0.4) but did not have a statistically-significant effect in the schizophrenia or bipolar groups. T. gondii had several nominally-significant positive associations, including the haplotypes HLA DRB∗03:01 ∼ HLA DQA∗05:01 ∼ HLA DQB∗02:01 and HLA B∗08:01 ∼ HLA C∗07:01.

CONCLUSIONS

We identified HLA types that showed strong and significant associations with neurotropic infections. Since some of these associations depended on mental illness status, the engagement of HLA-related pathways may be altered in schizophrenia due to immunogenetic differences or exposure history.

Bipolar disorder patients display reduced serum complement levels and elevated peripheral blood complement expression levels

OBJECTIVE

Bipolar disorder (BD) patients have recently been shown to exhibit increased proinflammatory cytokine levels indicating the role of inflammation in this disease. As inflammatory responses often include complement level alterations and complement production is influenced by cytokines, we aimed to find out whether complement system is activated in BD in a time-dependent manner and complement factors are involved in BD pathogenesis.

METHODS

Serum C4, factor B, sC5b-9 and neuron-specific enolase levels were measured by enzyme-linked immunosorbent assay, whereas peripheral blood mononuclear cell messenger RNA (mRNA) expression levels of C1q, C4, factor B and CD55 were measured by real-time polymerase chain reaction in chronic BD patients (n=22), first episode BD patients (n=24) and healthy controls (n=19).

RESULTS

Serum complement levels were significantly reduced in chronic BD patients as compared with first episode BD patients and healthy controls. Serum levels of complement factors showed significant inverse correlation with disease duration, severity of manic symptoms and serum neuron-specific enolase levels. In chronic BD patients, peripheral blood mononuclear cell mRNA expression levels of C1q, C4 and factor B were significantly elevated, whereas the mRNA expression level of the complement inhibitor CD55 was significantly reduced.

CONCLUSIONS

Our results suggest that complement factor levels are reduced in BD presumably due to overconsumption of the complement system and complement production is increased at mRNA level possibly as a compensation measure. Complement factors might potentially be used as indicators of disease severity, neuronal loss and cognitive dysfunction.