Complement C3 and C3aR mediate different aspects of emotional behaviours; relevance to risk for psychiatric disorder

Long-term GABA supplementation mitigates anxiety by modulating complement and neuroinflammatory pathways

Anxiety disorders are among the most prevalent mental health conditions, often linked with neuroinflammation and imbalances in neurotransmitter systems. This study examined the anxiolytic effects of oral GABA in chronic restraint stress (CRS) mice. Mice were divided into control, CRS, and two GABA-treated groups (10 mg/kg, 20 mg/kg). After 14 days of administration, anxiety-like behaviors were assessed using elevated-plus maze and open-field tests. GABA levels in the prefrontal cortex were quantified via ELISA, while anti-inflammatory cytokines were measured using an antibody array. Proteomic analysis of the hippocampus identified differentially expressed proteins, validated through Parallel Reaction Monitoring and immunoblotting. Results showed that GABA significantly alleviated anxiety-like behaviors, increased GABA levels in the prefrontal cortex, and elevated anti-inflammatory factors IL-10 and TGF-β1. Proteomic analysis and validation revealed GABA reversed complement dysregulation (C3, C4b, Cfh, Cfi). These findings suggest GABA alleviates anxiety by modulating immune homeostasis and complement activation, highlighting its therapeutic potential.

Plasma proteomic signature of chronic psychosocial stress in mice

Chronic stress significantly impacts both physical and mental wellbeing, increasing risk of cardiovascular disease, immune dysregulation, and psychiatric conditions such as depression and anxiety disorders. The plasma proteome is a valuable source of biomarkers of health and disease, but the limited number of studies exploring the potential of the plasma proteome as a biomarker for stress-related disorders underscores the importance of further investigation of the effects of chronic stress on the plasma proteome. The aim of this study was to examine the effect of a 5-week chronic psychosocial stress paradigm on the plasma proteome in mice and to determine if any affected proteins correlated with stress-induced changes in behaviour and physiology, and thus might represent biomarkers of negative impacts of chronic stress. Using LC-MS/MS proteomic analysis, 38 proteins in the mouse plasma proteome were identified to be affected by chronic psychosocial stress. Functional analysis revealed that these proteins clustered into biological functions including inflammatory response, regulation of the immune response, complement and coagulation cascades, lipid metabolic process, and high-density lipoprotein particles. Correlation analyses of the identified proteins with stress-induced behavioral or physiological changes stress revealed significant correlations between stress-induced anxiety-like behaviour and Phosphatidylinositol-glycan-specific phospholipase D, Complement C2, Epidermal growth factor receptor, Prosaposin, Actin-related protein 2/3 complex subunit 1B, Maltase-glucoamylase, Mannosyl-oligosaccharide 1,2-alpha-mannosidase IA and Fibrinogen-like protein 1. Chronic psychosocial stress blunted acute stress-induced corticosterone release, and this correlated with abundance of Pyrethroid hydrolase Ces2a; N-fatty-acyl-amino acid synthase/hydrolase Pm20d1, Mannosyl-oligosaccharide 1,2-alpha-mannosidase IA, Alpha-2-macroglobulin-P and L-selectin. Finally, stress-induced reductions in both brown and epididymal fat correlated with Phosphatidylinositol-glycan-specific phospholipase D, Complement C2, Epidermal growth factor receptor, Kininogen-1, Apolipoprotein M, Angiopoietin-related protein 3, Proprotein convertase subtilisin/kexin type 9, and Lipopolysaccharide-binding protein. These findings demonstrate that chronic psychosocial stress induces alterations in plasma proteins implicated in key biological processes and pathways related to stress response, immune function, and lipid metabolic regulation. Further investigation into these proteins may provide new avenues for identification of biomarkers or mediators of stress-induced pathology.

Immune transcriptomic profile in adult female pigs: dominance status has more influence than environmental enrichment

BACKGROUND

Assessing farm animals' welfare is crucial, yet practical physiological tools are still lacking. In this study, we tested whether the peripheral blood mononuclear cell (PBMC) transcriptome shows variations in association with sows' welfare. To do this, we compared animals whose welfare states were assumed to differ due to their lives in more or less enriched environments and to their different dominance statuses. Sows were housed in a conventional (C, n = 36) or enriched (E, n = 35) environments from gestation day 0 (G0) until three weeks before farrowing (G105), after which they were transferred to individual farrowing crates. From G99 to G103, behavioral analyses were conducted, and sows' dominance status was evaluated. A subset of 28 multiparous sows (C, n = 14 and E, n = 14) was selected for the collection of saliva on G35 and G98 and hair on G98 for cortisol measurement, and of blood samples for PBMC transcriptome analysis on G98 and on lactation day 12 (L12).

RESULTS

Both environmental enrichment (EE) and dominance status influenced cortisol and variables related to social and exploratory behavior, indicating an influence on sows' welfare. In the transcriptomic analysis, among the 12,260 genes submitted to differential analysis on G98, EE impacted 31 genes, while dominance status impacted 449 genes. Compared with subordinate sows (SUB), dominant (DOM) sows exhibited an upregulation of genes related to inflammatory process and plasma cell function, and downregulation of genes related to B-cell activation. In groups of sows, dominance status is partly related to sows' parity; therefore, we compared the effect of dominance with that of parity. Some common genes emerged when comparing high-parity (HP) vs. low-parity (LP) sows (542 differentially expressed genes (DEGs), including 180 in common with dominance-related genes), indicating that some effects of dominance on the transcriptome during gestation were in fact more due to age or reproductive cycles than to dominance itself. EE and dominance effects appeared relatively short-term, as DEG numbers decreased on L12 (four DEGs for E vs. C, 25 for DOM vs. SUB).

CONCLUSIONS

Dominance status exerted a more pronounced influence on sows' PBMC transcriptome than did environmental enrichment. In particular, dominance status modulated genes associated with B cells and plasma cell functions. Some of the genes identified in this study could be tested in the future as potential molecular markers of well-being.

Systemic Administration of a Site-Targeted Complement Inhibitor Attenuates Chronic Stress-Induced Social Behavior Deficits and Neuroinflammation in Mice

Chronic stress, a risk factor for many neuropsychiatric conditions, causes dysregulation in the immune system in both humans and animal models. Additionally, inflammation and synapse loss have been associated with deficits in social behavior. The complement system, a key player of innate immunity, has been linked to social behavior impairments caused by chronic stress. However, it is not known whether complement inhibition can help prevent neuroinflammation and behavioral deficits caused by chronic stress. In this study, we investigated the potential of a site-targeted complement inhibitor to ameliorate chronic stress-induced changes in social behavior and inflammatory markers in the prefrontal cortex (PFC) and hippocampus. Specifically, we investigated the use of C2-Crry, which comprises a natural antibody-derived single-chain antibody (ScFv) targeting domain-designated C2, linked to Crry, a C3 activation inhibitor. The C2 targeting domain recognizes danger-associated molecular patterns consisting of a subset of phospholipids that become exposed following cell stress or injury. We found that systemic administration of C2-Crry attenuated chronic stress-induced social behavioral impairments in mice. Furthermore, C2-Crry administration significantly decreased microglia/macrophage and astrocyte activation markers in the PFC and hippocampus. These findings suggest that site-targeted complement inhibition could offer a promising, safe, and effective strategy for treating chronic stress induced behavioral and immune function disorders.

Transcriptome Analysis Reveals Dynamic Microglial-Induced A1 Astrocyte Reactivity via C3/C3aR/NF-κB Signaling After Ischemic Stroke

Microglia and astrocytes are key players in neuroinflammation and ischemic stroke. A1 astrocytes are a subtype of astrocytes that are extremely neurotoxic and quickly kill neurons. Although the detrimental A1 astrocytes are present in many neurodegenerative diseases and are considered to accelerate neurodegeneration, their role in the pathophysiology of ischemic stroke is poorly understood. Here, we combined RNA-seq, molecular and immunological techniques, and behavioral tests to investigate the role of A1 astrocytes in the pathophysiology of ischemic stroke. We found that astrocyte phenotypes change from a beneficial A2 type in the acute phase to a detrimental A1 type in the chronic phase following ischemic stroke. The activated microglial IL1α, TNF, and C1q prompt commitment of A1 astrocytes. Inhibition of A1 astrocytes induction attenuates reactive gliosis and ameliorates morphological and functional defects following ischemic stroke. The crosstalk between astrocytic C3 and microglial C3aR contributes to the formation of A1 astrocytes and morphological and functional defects. In addition, NF-κB is activated following ischemic stroke and governs the formation of A1 astrocytes via direct targeting of inflammatory cytokines and chemokines. Taken together, we discovered that A2 astrocytes and A1 astrocytes are enriched in the acute and chronic phases of ischemic stroke respectively, and that the C3/C3aR/NF-κB signaling leads to A1 astrocytes induction. Therefore, the C3/C3aR/NF-κB signaling is a novel therapeutic target for ischemic stroke treatment.

Use of Extracellular Monomeric Ubiquitin as a Therapeutic Option for Major Depressive Disorder

Major depressive disorder (MDD) is a mood disorder that has become a global health emergency according to the World Health Organization (WHO). It affects 280 million people worldwide and is a leading cause of disability and financial loss. Patients with MDD present immunoendocrine alterations like cortisol resistance and inflammation, which are associated with alterations in neurotransmitter metabolism. There are currently numerous therapeutic options for patients with MDD; however, some studies suggest a high rate of therapeutic failure. There are multiple hypotheses explaining the pathophysiological mechanisms of MDD, in which several systems are involved, including the neuroendocrine and immune systems. In recent years, inflammation has become an important target for the development of new therapeutic options. Extracellular monomeric ubiquitin (emUb) is a molecule that has been shown to have immunomodulatory properties through several mechanisms including cholinergic modulation and the generation of regulatory T cells. In this perspective article, we highlight the influence of the inflammatory response in MDD. In addition, we review and discuss the evidence for the use of emUb contained in Transferon as a concomitant treatment with selective serotonin reuptake inhibitors (SSRIs).

Untargeted metabolomic, and proteomic analysis identifies metabolic biomarkers and pathway alterations in individuals with 22q11.2 deletion syndrome

INTRODUCTION

The chromosome 22q11.2 deletion syndrome (22q11.2DS) is characterized by a well-defined microdeletion and is associated with a wide range of brain-related phenotypes including schizophrenia spectrum disorders (SCZ), autism spectrum disorders (ASD), anxiety disorders and attention deficit disorders (ADHD). The typically deleted region in 22q11.2DS contains multiple genes which haploinsufficiency has the potential of altering the protein and the metabolic profiles.

OBJECTIVES

Alteration in metabolic processes and downstream protein pathways during the early brain development may help to explain the increased prevalence of the observed neurodevelopmental phenotypes in 22q11.2DS. However, relatively little is known about the correlation of dysregulated protein/metabolite expression and neurobehavioral impairments in individuals who developed them over time.

METHODS

In this study, we performed untargeted metabolic and proteomic analysis in plasma samples derived from 30 subjects including 16 participants with 22q11.2DS and 14 healthy controls (TD) enrolled in a longitudinal study, aiming to identify a metabolic and protein signature informing about the underlying mechanisms involved in disease development and progression. The metabolic and proteomic profiles were also compared between the participants with 22q11.2DS with and without various comorbidities, such as medical involvement, psychiatric conditions, and autism spectrum disorder (ASD) to detect potential changes among multiple specimens, collected overtime, with the aim to understand the basic underlying mechanisms involved in disease development and progression.

RESULTS

We observed a large number of statistically significant differences in metabolites between the two groups. Among them, the levels of taurine and arachidonic acid were significantly lower in 22q11.2DS compared to the TD group. In addition, we identified 16 proteins that showed significant changes in expression levels (adjusted P < 0.05) in 22q11.2DS as compared to TD, including those involved in 70 pathways such as gene expression, the PI3K-Akt signaling pathway and the complement system. Within participants with 22q11.2DS, no significant changes in those with and without medical or psychiatric conditions were observed.

CONCLUSION

To our knowledge, this is the first report on plasma metabolic and proteomic profiling and on the identification of unique biomarkers in 22q11.2DS. These findings may suggest the potential role of the identified metabolites and proteins as biomarkers for the onset of comorbid conditions in 22q11.2DS. Ultimately, the altered protein pathways in 22q11.2DS may provide insights of the biological mechanisms underlying the neurodevelopmental phenotype and may provide missing molecular outcome measures in future clinical trials to assess early-diagnosis treatment and the efficacy of response to targeted treatment.

CHD8 regulates gut epithelial cell function and affects autism-related behaviors through the gut-brain axis

Autism is a neurodevelopmental disorder characterized by early-onset social behavioral deficits and repetitive behaviors. Chromodomain helicase DNA-binding protein (CHD8) is among the genes most strongly associated with autism. In addition to the core behavioral symptoms of autism, affected individuals frequently present with gastrointestinal symptoms that are also common among individuals harboring mutations in the gene encoding CHD8. However, little is known regarding the mechanisms whereby CHD8 affects gut function. In addition, it remains unknown whether gastrointestinal manifestations contribute to the behavioral phenotypes of autism. The current study found that mice haploinsufficient for the large isoform of Chd8 (Chd8L) exhibited increased intestinal permeability, transcriptomic dysregulation in gut epithelial cells, reduced tuft cell and goblet cell counts in the gut, and an overall increase in microbial load. Gut epithelial cell-specific Chd8 haploinsufficiency was associated with increased anxiety-related behaviors together with a decrease in tuft cell numbers. Antibiotic treatment of Chd8L haploinsufficient mice attenuated social behavioral deficits. Together, these results suggest Chd8 as a key determinant of autism-related gastrointestinal deficits, while also laying the ground for future studies on the link between GI deficits and autism-related behaviors.

Role of innate immunity in SARS-CoV-2 infection

During severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, activated macrophages, dendritic cells (D.C.), neutrophils, and natural killer (N.K.) cells are the first defense against infection. These immune effectors trap and ingest the virus, kill infected epithelial cells, or produce anti-viral cytokines. Evidence suggests that aging, obesity, and mental illness can lead to weakened innate immunity and, thus, are all associated with elevated infection and severe disease progression of coronavirus disease 2019 (COVID-19). Innate immune defense networks play a fundamental role in suppressing viral replication, infection establishment, and viral pathogenesis of SARS-CoV-2 and other respiratory viruses.

Stressed Microglia: Neuroendocrine-Neuroimmune Interactions in the Stress Response

Stressful life experiences are associated with the development of neuropsychiatric disorders like depression. Emerging evidence indicates that microglia, the specialized resident macrophages of the brain, may be a key mediator of the relationship between psychosocial stressor exposure and adaptive or maladaptive responses at the level of synaptic, circuit, and neuroimmune alterations. Here, we review current literature regarding how psychosocial stressor exposure changes microglial structure and function, thereby altering behavioral and brain outcomes, with a particular focus on age- and sex-dependent effects. We argue that additional emphasis should be placed in future research on investigating sex differences and the impacts of stressor exposure during sensitive periods of development, as well as going beyond traditional morphological measurements to interrogate microglial function. The bidirectional relationship between microglia and the stress response, particularly the role of microglia in the neuroendocrine control of stress-related circuits, is also an important area for future investigation. Finally, we discuss emerging themes and future directions that point to the possibility of the development of novel therapeutics for stress-related neuropsychiatric disorders.

Brain regional pharmacokinetics of hydroxytyrosol and its molecular mechanism against depression assessed by multi-omics approaches

BACKGROUND

Hydroxytyrosol (HT), as the main compound in olive leaves with its potential ability to cross blood-brain barrier (BBB), has exhibited the advantaged antidepressant effect. However, no information is available regarding the brain regional uptake of HT, as well the underlying antidepressant mechanism remains unclear.

PURPOSE

To comprehensively reveal the brain uptake of HT and its specific mechanism on the accompanying antidepressant activity.

STUDY DESIGN AND METHODS

The BBB penetration and brain regional distribution of HT in the normal and chronic unpredictable mild stress (CUMS)-induced depressive mice in consideration with the BBB integrality were analyzed. Then, the hippocampal region-specific responses of biomolecules and concurrent alterations in the therapeutic effect of HT on depression were explored using untargeted metabolomics, spatial-resolved metabolomics and tissue proteomics, which were confirmed by LPS-induced BV-2 microglia and CUMS mice.

RESULTS

BBB permeability analysis in normal and CUMS mice confirmed that increased BBB permeability of CUMS mice was induced by the deficiency of tight junction-related proteins. Consistently, according to the established LC-MS/MS method, it was found that HT could not be largely detected in the cerebrospinal fluids and brains of normal mice after oral administration, while it could excessively penetrate the BBB (200-fold higher), and mostly distributed in the hippocampus of CUMS mice. Meanwhile, multi-omics analysis combined with targeted analysis discovered that HT could mainly improve fatty acid biosynthesis and metabolism in the hippocampus with region-specific responses and accompanying inhibition of C3-CD11b pathway in CUMS mice. Besides, in vitro experiments further confirmed the anti-complement ability of HT, which could inhibit C3-CD11b pathway for alleviating the LPS-induced BV-2 microglia activation.

CONCLUSION

HT can excessively penetrate the BBB and be mostly distributed in the hippocampus of depressive mice, which contribute to improve fatty acid biosynthesis and metabolism in the hippocampus with region-specific responses and accompanying inhibition of C3-CD11b pathway for microglia activation. These findings give the clearer understanding of brain regional pharmacokinetics of HT and its accompanying molecular mechanism against depression.

Immunomodulatory and Anti-inflammatory effect of Neural Stem/Progenitor Cells in the Central Nervous System

Neuroinflammation is a critical event that responds to disturbed homeostasis and governs various neurological diseases in the central nervous system (CNS). The excessive inflammatory microenvironment in the CNS can adversely affect endogenous neural stem cells, thereby impeding neural self-repair. Therapies with neural stem/progenitor cells (NSPCs) have shown significant inhibitory effects on inflammation, which is mainly achieved through intercellular contact and paracrine signalings. The intercellular contact between NSPCs and immune cells, the activated CNS- resident microglia, and astrocyte plays a critical role in the therapeutic NSPCs homing and immunomodulatory effects. Moreover, the paracrine effect mainly regulates infiltrating innate and adaptive immune cells, activated microglia, and astrocyte through the secretion of bioactive molecules and extracellular vesicles. However, the molecular mechanism involved in the immunomodulatory effect of NSPCs is not well discussed. This article provides a systematic analysis of the immunomodulatory mechanism of NSPCs, discusses efficient ways to enhance its immunomodulatory ability, and gives suggestions on clinical therapy.

Contribution of animal models to the mechanistic understanding of Alternative Pathway and Amplification Loop (AP/AL)-driven Complement-mediated Diseases

This review aimed to capture the key findings that animal models have provided around the role of the alternative pathway and amplification loop (AP/AL) in disease. Animal models, particularly mouse models, have been incredibly useful to define the role of complement and the alternative pathway in health and disease; for instance, the use of cobra venom factor and depletion of C3 provided the initial insight that complement was essential to generate an appropriate adaptive immune response. The development of knockout mice have further underlined the importance of the AP/AL in disease, with the FH knockout mouse paving the way for the first anti-complement drugs. The impact from the development of FB, properdin, and C3 knockout mice closely follows this in terms of mechanistic understanding in disease. Indeed, our current understanding that complement plays a role in most conditions at one level or another is rooted in many of these in vivo studies. That C3, in particular, has roles beyond the obvious in innate and adaptive immunity, normal physiology, and cellular functions, with or without other recognized AP components, we would argue, only extends the reach of this arm of the complement system. Humanized mouse models also continue to play their part. Here, we argue that the animal models developed over the last few decades have truly helped define the role of the AP/AL in disease.

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.

Exercise modulates central and peripheral inflammatory responses and ameliorates methamphetamine-induced anxiety-like symptoms in mice

Anxiety-like symptoms are common symptoms of methamphetamine (METH) users, especially in the acute withdrawal period, which is an important factor for the high relapse rate during METH acute withdrawal. Exercise has been demonstrated to relieve anxiety-like symptoms during METH withdrawal, but the underlying mechanisms of this anti-anxiety effect are still unclear. Activated microglia and abnormal neuroinflammation play an important role in the pathogenesis of anxiety-like symptoms after METH withdrawal. Moreover, peripheral immune factors were also significantly associated with anxiety symptoms. However, the effects of treadmill exercise on microglial function and neuroinflammation in the striatum and hippocampus during acute METH withdrawal have not been reported. In the current study, we found severe peripheral immune dysfunction in METH users during acute withdrawal, which may in part contribute to anxiety symptoms during METH acute withdrawal. We also showed that 2 weeks of METH exposure induced anxiety-like symptoms in the acute withdrawal period. Additionally, METH exposure resulted in increased microglial activation and proinflammatory cytokines released in the mouse striatum and hippocampus during acute withdrawal. We next evaluated the effects of treadmill exercise in countering anxiety-like symptoms induced by METH acute withdrawal. The results showed that anxiety-like symptoms induced by acute METH withdrawal were attenuated by coadministration of treadmill exercise. In addition, treadmill exercise counteracted METH-induced microglial activation in the mouse striatum and various subregions of the hippocampus. Furthermore, treadmill exercise also reversed the increase in proinflammatory cytokines induced by acute METH withdrawal in the mouse striatum, hippocampus and serum. Our findings suggest that the anti-anxiety effect of treadmill exercise may be mediated by reducing microglial activation and regulating central and peripheral inflammatory responses.

Complement Dependent Synaptic Reorganisation During Critical Periods of Brain Development and Risk for Psychiatric Disorder

We now know that the immune system plays a major role in the complex processes underlying brain development throughout the lifespan, carrying out a number of important homeostatic functions under physiological conditions in the absence of pathological inflammation or infection. In particular, complement-mediated synaptic pruning during critical periods of early life may play a key role in shaping brain development and subsequent risk for psychopathology, including neurodevelopmental disorders such as schizophrenia and autism spectrum disorders. However, these disorders vary greatly in their onset, disease course, and prevalence amongst sexes suggesting complex interactions between the immune system, sex and the unique developmental trajectories of circuitries underlying different brain functions which are yet to be fully understood. Perturbations of homeostatic neuroimmune interactions during different critical periods in which regional circuits mature may have a plethora of long-term consequences for psychiatric phenotypes, but at present there is a gap in our understanding of how these mechanisms may impact on the structural and functional changes occurring in the brain at different developmental stages. In this article we will consider the latest developments in the field of complement mediated synaptic pruning where our understanding is beginning to move beyond the visual system where this process was first described, to brain areas and developmental periods of potential relevance to psychiatric disorders.