Plasma complement component 4 alterations in patients with schizophrenia before and after antipsychotic treatment

Association of elevated levels of peripheral complement components with cortical thinning and impaired logical memory in drug-naïve patients with first-episode schizophrenia

Schizophrenia has been linked to polymorphism in genes encoding components of the complement system, and hyperactive complement activity has been linked to immune dysfunction in schizophrenia patients. Whether and how specific complement components influence brain structure and cognition in the disease is unclear. Here we compared 52 drug-naïve patients with first-episode schizophrenia and 52 healthy controls in terms of levels of peripheral complement factors, cortical thickness (CT), logical memory and psychotic symptoms. We also explored the relationship between complement factors with CT, cognition and psychotic symptoms. Patients showed significantly higher levels of C1q, C4, factor B, factor H, and properdin in plasma. Among patients, higher levels of C3 in plasma were associated with worse memory recall, while higher levels of C4, factor B and factor H were associated with thinner sensory cortex. These findings link dysregulation of specific complement components to abnormal brain structure and cognition in schizophrenia.

Microglial contribution to the pathology of neurodevelopmental disorders in humans

Microglia are the brain's resident macrophages, which guide various developmental processes crucial for brain maturation, activity, and plasticity. Microglial progenitors enter the telencephalic wall by the 4th postconceptional week and colonise the fetal brain in a manner that spatiotemporally tracks key neurodevelopmental processes in humans. However, much of what we know about how microglia shape neurodevelopment comes from rodent studies. Multiple differences exist between human and rodent microglia warranting further focus on the human condition, particularly as microglia are emerging as critically involved in the pathological signature of various cognitive and neurodevelopmental disorders. In this article, we review the evidence supporting microglial involvement in basic neurodevelopmental processes by focusing on the human species. We next concur on the neuropathological evidence demonstrating whether and how microglia contribute to the aetiology of two neurodevelopmental disorders: autism spectrum conditions and schizophrenia. Next, we highlight how recent technologies have revolutionised our understanding of microglial biology with a focus on how these tools can help us elucidate at unprecedented resolution the links between microglia and neurodevelopmental disorders. We conclude by reviewing which current treatment approaches have shown most promise towards targeting microglia in neurodevelopmental disorders and suggest novel avenues for future consideration.

Peripheral Complement Factor-Based Biomarkers for Patients with First-Episode Schizophrenia

Objective

Schizophrenia (SCZ) is a severe, protracted neurological disorder that causes disruptive conduct in millions of individuals globally. Discovery of potential biomarkers in clinical settings would lead to the development of efficient diagnostic techniques and an awareness of the disease's pathogenesis and prognosis. The aim of the present study was to discover and identify serum complement factor-based biomarkers in discriminating patients with first-episode SCZ from healthy controls.

Methods

Eighty-nine patients with first-episode SCZ and 89 healthy controls were included in this study. Psychiatric symptom severity of patients with SCZ was measured with the Brief Psychiatric Rating Scale-18 Item Version (BPRS) and the Scales for the Assessment of Negative/Positive Symptoms (SANS/SAPS). A total of 5 complement factors including complement component 1 (C1), C2, C3, C4, and 50% hemolytic complement (CH50) were measured using commercially available enzyme-linked immunosorbent assay (ELISA) kits. The levels of serum complement factors in the SCZ and control groups were compared, and the receiver operating characteristic (ROC) curve method was used to assess the diagnostic values of various complement factors for separating SCZ patients from healthy controls. Pearson's correlation test was used to assess the relationships between serum complement factor concentrations and the psychiatric symptom severity.

Results

There was an increase in serum levels of C1, C2, C3, C4, and CH50 among patients with SCZ. Moreover, based on ROC curve analysis, the AUC value of a combined panel of C1, C2, C3, C4, and CH50 was 0.857 when used to discriminate patients with SCZ from healthy controls. Furthermore, serum C2, C3, and CH50 levels were positively correlated to the scores of SANS, SAPS, and BPRS in patients with SCZ, respectively.

Conclusion

These results suggested that circulating complement factors including C1, C2, C3, C4, and CH50 may have potential in discovering biomarkers for diagnosing first-episode SCZ.

Identifying novel proteins underlying schizophrenia via integrating pQTLs of the plasma, CSF, and brain with GWAS summary data

BACKGROUND

Schizophrenia (SCZ) is a chronic and severe mental illness with no cure so far. Mendelian randomization (MR) is a genetic method widely used to explore etiologies of complex traits. In the current study, we aimed to identify novel proteins underlying SCZ with a systematic analytical approach.

METHODS

We integrated protein quantitative trait loci (pQTLs) of the brain, cerebrospinal fluid (CSF), and plasma with the latest and largest SCZ genome-wide association study (GWAS) via a systematic analytical framework, including two-sample MR analysis, Steiger filtering analysis, and Bayesian colocalization analysis.

RESULTS

The genetically determined protein level of C4A/C4B (OR = 0.70, p = 1.66E-07) in the brain and ACP5 (OR = 0.42, p = 3.73E-05), CNTN2 (OR = 0.62, p = 2.57E-04), and PLA2G7 (OR = 0.71, p = 1.48E-04) in the CSF was associated with a lower risk of SCZ, while the genetically determined protein level of TIE1 (OR = 3.46, p = 4.76E-05), BCL6 (OR = 3.63, p = 1.59E-07), and MICB (OR = 4.49, p = 2.31E-11) in the CSF were associated with an increased risk for SCZ. Pathway enrichment analysis indicated that genetically determined proteins suggestively associated with SCZ were enriched in the biological process of the immune response.

CONCLUSION

In conclusion, we identified one protein in the brain and six proteins in the CSF that showed supporting evidence of being potentially associated with SCZ, which could provide insights into future mechanistic studies to find new treatments for the disease. Our results also supported the important role of neuroinflammation in the pathogenesis of SCZ.

Alterations in innate immune defense distinguish first-episode schizophrenia patients from healthy controls

Innate immune components involved in host defense have been implicated in schizophrenia (SCZ). However, studies exploring their clinical utility in SCZ diagnosis are limited. The main purpose of this study was to evaluate whether circulating endotoxin, high mobility group box 1 protein (HMGB1) and complement component 4 (C4) could act as peripheral biomarkers to distinguish first-episode schizophrenia (FES, n = 42) patients from healthy controls (HCs, n = 35) in associations with psychopathological symptoms and cognitive dysfunctions. Also, their changes after 8-week antipsychotic treatment were investigated. The Positive and Negative Syndrome Scale (PANSS), Psychotic Symptom Rating Scale (PSYRATS), and MATRICS Consensus Cognitive Battery (MCCB) were administered. Receiver operating characteristic (ROC) curves were conducted to evaluate the diagnostic effectiveness of the three biological indicators. Compared to HCs, levels of endotoxin, HMGB1, and C4 were remarkably increased in FES patients after controlling for age, gender, body mass index (BMI) and education years, and the combination of the three biomarkers demonstrated desirable diagnostic performance (AUC = 0.933). Moreover, the endotoxin level was positively correlated with the severity of auditory hallucinations. After 8 weeks of treatment, HMGB1 was decreased significantly in patients but still higher than that in HCs, whereas endotoxin and C4 did not change statistically. The baseline levels of endotoxin, HMGB1, and C4, as well as their changes were not associated with changes in any PANSS subscale score and total score. Our preliminary results suggest that a composite peripheral biomarker of endotoxin, HMGB1, and C4 may have accessory diagnostic value to distinguish SCZ patients from HCs. Additionally, endotoxin might be implicated in the pathogenesis of auditory hallucinations.