The role of the complement system in Multiple Sclerosis: A review

Fluid Biomarkers in Demyelinating Spectrum Disorders: Past, Present, and Prospects

The diagnostic algorithm for the demyelinating disorders of the central nervous system remains a work in progress, with the search for the ideal biomarkers ongoing. The so-called "ideal" biomarker should ensure the accurate differentiation between the most common demyelinating pathologies of the CNS and between the subtypes of the same pathology (for example, the conversion from relapsing-remitting multiple sclerosis to the secondary progressive phenotype). Advances in technology facilitated this research and in the following sections we will comprehensively review most of these, outlining the past, present, and prospects and the impact they had on both diagnosis and therapeutic approach.

Human Umbilical Cord Mesenchymal Stem Cell-Derived Exosomes Boost Functional Performance in an Animal Model of Multiple Sclerosis Through Recruiting Oligodendrocytes and Attenuating Gliosis

BACKGROUND

Multiple sclerosis (MS) is a chronic neuroinflammatory and demyelinating condition that causes movement problems due to a probable failure to differentiate oligodendrocyte precursor cells into myelinating oligodendrocytes.

AIMS

This work aims to evaluate the effect of exosomes derived from human umbilical cord mesenchymal stem cells on functional recovery in an animal model of multiple sclerosis.

METHODS

The adult male C57BL/6J mice were randomly divided into three groups. The control mice were provided with a standard diet (CONT group). The chronically demyelinated (CPZ) group was fed a 0.2% cuprizone diet for 12 weeks. In the third group, mice received exosomes weekly for three weeks following chronic demyelination (Exo/CPZ group). The mice in the groups were tested weekly for mobility using a beam walking test (BWT), and their corpus callosum was studied histologically, immunohistochemically, and molecularly.

RESULTS

According to BWT results, hucMSC-Exos enhanced motor function in mice following cuprizone intoxication. Histological staining revealed a substantial increase in remyelination in the corpus callosum. Moreover, immunohistochemical tests revealed that hucMSC-Exos lowered the level of demyelination and improved glial response by lowering the number of microglia and astrocytes. In addition, hucMSC-Exos also upregulated the expression of genes associated with the oligodendrocyte lineage.

CONCLUSIONS

hucMSC-Exos administration in the animal model of chronic MS leads to improved movement function, likely due to increased remyelination, modulation of inflammatory processes, and increased expression of genes related to the oligodendrocyte lineage. Therefore, using hucMSC-Exos seems to be a promising treatment strategy for demyelinating illnesses such as MS.

Dynamic Proteome Changes in Cuprizone-Induced Demyelination and Remyelination in the Mouse Brain

This study aimed to gain insights into the dynamic proteome changes and underlying molecular mechanisms of de/remyelination in a cuprizone model, a widely used preclinical model of multiple sclerosis (MS). Longitudinal sampling of control or cuprizone-treated mouse brains was executed at 6 time points over 6 weeks. Data analysis included 8489 quantified proteins. Differential proteomic and GO analyses revealed that 5.9% of the quantified proteome was altered, including reported and novel de/remyelination-relevant protein changes and underlying pathways. We found that oligodendrocyte proteins (Fa2h and Ugt8) were significantly changed during demyelination, suggesting that dysregulated sphingolipid metabolism in MS may stem from oligodendrocyte pathology. Importantly, we showed that the cholesterol biosynthesis pathway was the most enriched biological process in a subset of significantly changed proteins, where myelination was highly enriched. We further validated the changes in the cholesterol biosynthesis pathway through targeted GC-MS analysis of intermediate sterols, supporting the critical role of cholesterol biosynthesis in de/remyelination. Unexpectedly, changes of myelin-associated proteins, Mbp and Plp1, were minimal, while Ermn showed significant reduction tracking with demyelination, indicating that some myelin protein changes are more sensitive to demyelination. Together with a list of significantly altered proteins, the results of this study could benefit future remyelination research.

Neuroimmune crosstalk in chronic neuroinflammation: microglial interactions and immune modulation

Neuroinflammation is a fundamental feature of many chronic neurodegenerative diseases, where it contributes to disease onset, progression, and severity. This persistent inflammatory state arises from the activation of innate and adaptive immune responses within the central nervous system (CNS), orchestrated by a complex interplay of resident immune cells, infiltrating peripheral immune cells, and an array of molecular mediators such as cytokines, chemokines, and extracellular vesicles. Among CNS-resident cells, microglia play a central role, exhibiting a dynamic spectrum of phenotypes ranging from neuroprotective to neurotoxic. In chronic neurodegenerative diseases, sustained microglial activation often leads to the amplification of inflammatory cascades, reinforcing a pathogenic cycle of immune-mediated damage. Intercellular communication within the inflamed CNS is central to the persistence and progression of neuroinflammation. Microglia engage in extensive crosstalk with astrocytes, neurons, oligodendrocytes, and infiltrating immune cells, shaping both local and systemic inflammatory responses. These interactions influence key processes such as synaptic pruning, phagocytosis, blood-brain barrier integrity, and cytokine-mediated signaling. Understanding the mechanisms of cell-cell signaling in this context is critical for identifying therapeutic strategies to modulate the immune response and restore homeostasis. This review explores the key players in CNS neuroinflammation, with a focus on the role of microglia, the molecular pathways underlying intercellular communication, and potential therapeutic approaches to mitigate neuroinflammatory damage in chronic neurodegenerative diseases.

Cathepsin C exacerbates EAE by promoting the expansion of Tfh cells and the formation of TLSs in the CNS

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) mediated by CD4+ T helper (Th) cells, and characterized by immune cell infiltration, demyelination and neurodegeneration, with no definitive cure available. Thus, it is pivotal and imperative to acquire more profound comprehension of the underlying mechanisms implicated in MS. Dysregulated immune responses are widely believed to play a primary role in the pathogenesis of MS. Recently, a plethora of studies have demonstrated the involvement of T follicular helper (Tfh) cells and tertiary lymphoid-like structures (TLSs) in the pathogenesis and progression of MS. Cathepsin C (CatC) is a cysteine exopeptidase which is crucial for the activation of immune-cell-associated serine proteinases in many inflammatory diseases in peripheral system, such as rheumatoid arthritis and septicemia. We have previously demonstrated that CatC is involved in neuroinflammation and exacerbates demyelination in both cuprizone-induced and experimental autoimmune encephalomyelitis (EAE) mouse models. However, the underlying immunopathological mechanism remains elusive. In the present study, we established a recombinant myelin oligodendrocyte glycoprotein 35-55 peptide-induced EAE model using conditional CatC overexpression mice to investigate the effects of CatC on the alteration of CD4+ Th subsets, including Th1, Th2, Th17, Tfh and T regulatory cells. Our findings demonstrated that CatC particularly enhanced the population of Tfh cell in the brain, resulting in the earlier onset and more severe chronic syndrome of EAE. Furthermore, CatC promoted the formation of TLSs in the brain, leading to persistent neuroinflammation and exacerbating the severity of EAE in the chronic phase. Conversely, treatment with AZD7986, a specific inhibitor of CatC, effectively attenuated the syndrome of EAE and its effects caused by CatC both in vivo and in vitro. These findings provide a novel insight into the critical role of CatC in innate and adaptive immunity in EAE, and specific inhibitor of CatC, AZD7986, may contribute to potential therapeutic strategies for MS.

Deletion of Card9 eliminates the detrimental facets of mycobacterial adjuvants

Although mycobacterial adjuvants are capable of eliciting a strong adaptive humoral and cellular immunity, they also sometimes provoke detrimental outcomes, including autoimmune/inflammatory syndromes. Here, we show that the deletion of caspase recruitment domain family member 9 (Card9), a signaling adaptor of a set of innate immune receptors, can eliminate the detrimental effects of mycobacterial adjuvants. Long-lasting tissue-destructive skin inflammation at the site of complete Freund's adjuvant (CFA) injection, lung granuloma formation induced by intratracheal Mycobacterium bovis Bacillus Calmette-Guérin infection, and the incidence and severity of experimental autoimmune encephalomyelitis and collagen-induced arthritis induced by autoantigen immunization with CFA were considerably attenuated in Card9-deficient (Card9 -/- ) mice compared to control wild-type mice. Card9 -/- mice showed impaired development of Th17, but not Th1, in the early phase after autoimmune induction, due to the impaired development of IL-6-producing Sirpαhigh dendritic cells, which are essential for priming pathigenic Th17, in the draining lymph nodes. However, Card9 deletion did not affect overall adaptive antibody production or delayed-type hypersensitivity following immunization with CFA, indicating that humoral and type 1 immune responses remained intact. These results suggest that avoiding the activation of Card9 signaling during vaccination with mycobacteria-containing vaccines may mitigate the risk of detrimental type 3 immune responses, while preserving type 1 immune responses that are effective against intracellular pathogens and cancers.

Immunoglobulin G and Complement as Major Players in the Neurodegeneration of Multiple Sclerosis

Multiple Sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system (CNS) and is termed as one of the most common causes of neurological disability in young adults. Axonal loss and neuronal cell damage are the primary causes of disease progression and disability. Yet, little is known about the mechanism of neurodegeneration in the disease, a limitation that impairs the development of more effective treatments for progressive MS. MS is characterized by the presence of oligoclonal bands and raised levels of immunoglobulins in the CNS. The role of complement in the demyelinating process has been detected in both experimental animal models of MS and within the CNS of affected MS patients. Furthermore, both IgG antibodies and complement activation can be detected in the demyelinating plaques and cortical gray matter lesions. We propose here that both immunoglobulins and complement play an active role in the neurodegenerative process of MS. We hypothesize that the increased CNS IgG antibodies form IgG aggregates and bind complement C1q with high affinity, activating the classical complement pathway. This results in neuronal cell damage, which leads to neurodegeneration and demyelination in MS.

circRNAs as Epigenetic Regulators of Integrity in Blood-Brain Barrier Architecture: Mechanisms and Therapeutic Strategies in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory neurodegenerative disease leading to progressive demyelination and neuronal loss, with extensive neurological symptoms. As one of the most widespread neurodegenerative disorders, with an age onset of about 30 years, it turns out to be a socio-health and economic issue, thus necessitating therapeutic interventions currently unavailable. Loss of integrity in the blood-brain barrier (BBB) is one of the distinct MS hallmarks. Brain homeostasis is ensured by an endothelial cell-based monolayer at the interface between the central nervous system (CNS) and systemic bloodstream, acting as a selective barrier. MS results in enhanced barrier permeability, mainly due to the breakdown of tight (TJs) and adherens junctions (AJs) between endothelial cells. Specifically, proinflammatory mediator release causes failure in cytoplasmic exposure of junctions, resulting in compromised BBB integrity that enables blood cells to cross the barrier, establishing iron deposition and neuronal impairment. Cells with a compromised cytoskeletal protein network, fiber reorganization, and discontinuous junction structure can occur, resulting in BBB dysfunction. Recent investigations on spatial transcriptomics have proven circularRNAs (circRNAs) to be powerful multi-functional molecules able to epigenetically regulate transcription and structurally support proteins. In the present review, we provide an overview of the recent role ascribed to circRNAs in maintaining BBB integrity/permeability via cytoskeletal stability. Increased knowledge of the mechanisms responsible for impairment and circRNA's role in driving BBB damage and dysfunction might be helpful for the recognition of novel therapeutic targets to overcome BBB damage and unrestrained neurodegeneration.

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.

Association of Complement Factors With Disability Progression in Primary Progressive Multiple Sclerosis

BACKGROUND AND OBJECTIVES

The complement system is known to play a role in multiple sclerosis (MS) pathogenesis. However, its contribution to disease progression remains elusive. The study investigated the role of the complement system in disability progression of patients with primary progressive MS (PPMS).

METHODS

Sixty-eight patients with PPMS from 12 European MS centers were included in the study. Serum and CSF levels of a panel of complement components (CCs) were measured by multiplex enzyme-linked immunosorbent assay at a baseline time point (i.e., sampling). Mean (SD) follow-up time from baseline was 9.6 (4.8) years. Only one patient (1.5%) was treated during follow-up. Univariable and multivariable logistic regressions adjusted for age, sex, and albumin quotient were performed to assess the association between baseline CC levels and disability progression in short term (2 years), medium term (6 years), and long term (at the time of the last follow-up).

RESULTS

In short term, CC played little or no role in disability progression. In medium term, an elevated serum C3a/C3 ratio was associated with a higher risk of disability progression (adjusted OR 2.30; 95% CI 1.17-6.03; p = 0.040). By contrast, increased CSF C1q levels were associated with a trend toward reduced risk of disability progression (adjusted OR 0.43; 95% CI 0.17-0.98; p = 0.054). Similarly, in long term, an elevated serum C3a/C3 ratio was associated with higher risk of disability progression (adjusted OR 1.81; 95% CI 1.09-3.40; p = 0.037), and increased CSF C1q levels predicted lower disability progression (adjusted OR 0.41; 95% CI 0.17-0.86; p = 0.025).

DISCUSSION

Proteins involved in the activation of early complement cascades play a role in disability progression as risk (elevated serum C3a/C3 ratio) or protective (elevated CSF C1q) factors after 6 or more years of follow-up in patients with PPMS. The protective effects associated with C1q levels in CSF may be related to its neuroprotective and anti-inflammatory properties.

The causal relationship between autoimmune diseases and age-related macular degeneration: A two-sample mendelian randomization study

OBJECTIVE

The aim of this study is to investigate the potential causal relationship between autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, and Type 1 diabetes, and age-related macular degeneration (AMD). By utilizing the two-sample Mendelian Randomization (MR) approach, we endeavor to address this complex medical issue.

METHODS

Genome-wide association study (GWAS) data for autoimmune diseases and AMD were obtained from the IEU Open GWAS database and the FinnGen consortium. A series of stringent SNP filtering steps was applied to ensure the reliability of the genetic instruments. MR analyses were conducted using the TwoSampleMR and MR-PRESSO packages in R. The inverse-variance weighted (IVW) method served as the primary analysis, complemented by multiple supplementary analyses and sensitivity tests.

RESULTS

Within the discovery sample, only a statistically significant inverse causal relationship between multiple sclerosis (MS) and AMD was observed (OR = 0.92, 95% CI: 0.88-0.97, P = 0.003). This finding was confirmed in the replication sample (OR = 0.85, 95% CI: 0.80-0.89, P = 3.32×10-12). No statistically significant associations were detected between systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, and Type 1 diabetes and AMD.

CONCLUSION

Strong evidence is provided by this study to support the existence of an inverse causal relationship between multiple sclerosis and age-related macular degeneration. However, no causal evidence was found linking other autoimmune diseases with AMD. These findings not only offer novel insights into the potential etiological mechanisms underlying AMD but also suggest possible directions for future clinical interventions.

The potential application of complement inhibitors-loaded nanosystem for autoimmune diseases via regulation immune balance

The complement is an important arm of the innate immune system, once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammation. Recent studies have shown that over-activated complement is the main proinflammatory system of autoimmune diseases (ADs). In addition, activated complements interact with autoantibodies, immune cells exacerbate inflammation, further worsening ADs. With the increasing threat of ADs to human health, complement-based immunotherapy has attracted wide attention. Nevertheless, efficient and targeted delivery of complement inhibitors remains a significant challenge owing to their inherent poor targeting, degradability, and low bioavailability. Nanosystems offer innovative solutions to surmount these obstacles and amplify the potency of complement inhibitors. This prime aim to present the current knowledge of complement in ADs, analyse the function of complement in the pathogenesis and treatment of ADs, we underscore the current situation of nanosystems assisting complement inhibitors in the treatment of ADs. Considering technological, physiological, and clinical validation challenges, we critically appraise the challenges for successfully translating the findings of preclinical studies of these nanosystem assisted-complement inhibitors into the clinic, and future perspectives were also summarised. (The graphical abstract is by BioRender.).

Microglia phagocytic mechanisms: Development informing disease

Microglia are tissue-resident macrophages and professional phagocytes of the central nervous system (CNS). In development, microglia-mediated phagocytosis is important for sculpting the cellular architecture. This includes the engulfment of dead/dying cells, pruning extranumerary synapses and axons, and phagocytosing fragments of myelin sheaths. Intriguingly, these developmental phagocytic mechanisms by which microglia sculpt the CNS are now appreciated as important for eliminating synapses, myelin, and proteins during neurodegeneration. Here, we discuss parallels between neurodevelopment and neurodegeneration, which highlights how development is informing disease. We further discuss recent advances and challenges towards therapeutically targeting these phagocytic pathways and how we can leverage development to overcome these challenges.

Immune System Dysregulation in the Progression of Multiple Sclerosis: Molecular Insights and Therapeutic Implications

Multiple sclerosis (MS), a prevalent neurological disorder, predominantly affects young adults and is characterized by chronic autoimmune activity. The study explores the immune system dysregulation in MS, highlighting the crucial roles of immune and non-neuronal cells in the disease's progression. This review examines the dual role of cytokines, with some like IL-6, TNF-α, and interferon-gamma (IFN-γ) promoting inflammation and CNS tissue injury, and others such as IL-4, IL-10, IL-37, and TGF-β fostering remyelination and protecting against MS. Elevated chemokine levels in the cerebrospinal fluid (CSF), including CCL2, CCL5, CXCL10, CXCL13, and fractalkine, are analyzed for their role in facilitating immune cell migration across the blood-brain barrier (BBB), worsening inflammation and neurodegeneration. The study also delves into the impact of auto-antibodies targeting myelin components like MOG and AQP4, which activate complement cascades leading to further myelin destruction. The article discusses how compromised BBB integrity allows immune cells and inflammatory mediators to infiltrate the CNS, intensifying MS symptoms. It also examines the involvement of astrocytes, microglia, and oligodendrocytes in the disease's progression. Additionally, the effectiveness of immunomodulatory drugs such as IFN-β and CD20-targeting monoclonal antibodies (e.g., rituximab) in modulating immune responses is reviewed, highlighting their potential to reduce relapse rates and delaying MS progression. These insights emphasize the importance of immune system dysfunction in MS development and progression, guiding the development of new therapeutic strategies. The study underscores recent advancements in understanding MS's molecular pathways, opening avenues for more targeted and effective treatments.

Targeted-Neuroinflammation Mitigation Using Inflammasome-Inhibiting Nanoligomers is Therapeutic in an Experimental Autoimmune Encephalomyelitis Mouse Model

Multiple sclerosis (MS) is a debilitating autoimmune disease that impacts millions of patients worldwide, disproportionately impacting women (4:1), and often presenting at highly productive stages of life. This disease affects the spinal cord and brain and is characterized by severe neuroinflammation, demyelination, and subsequent neuronal damage, resulting in symptoms like loss of mobility. While untargeted and pan-immunosuppressive therapies have proven to be disease-modifying and manage (or prolong the time between) symptoms in many patients, a significant fraction are unable to achieve remission. Recent work has suggested that targeted neuroinflammation mitigation through selective inflammasome inhibition can offer relief to patients while preserving key components of immune function. Here, we show a screening of potential therapeutic targets using inflammasome-inhibiting Nanoligomers (NF-κB1, TNFR1, TNF-α, IL-6) that meet or far-exceed commercially available small-molecule counterparts like ruxolitinib, MCC950, and deucravacitinib. Using the human brain organoid model, top Nanoligomer combinations (NF-κB1 + TNFR1: NI111, and NF-κB1 + NLRP3: NI112) were shown to significantly reduce neuroinflammation without any observable negative impact on organoid function. Further testing of these top Nanoligomer combinations in an aggressive experimental autoimmune encephalomyelitis (EAE) mouse model for MS using intraperitoneal (IP) injections showed that NF-κB1 and NLRP3 targeting Nanoligomer combination NI112 rescues mice without observable loss of mobility or disability, minimal inflammation in brain and spinal cord histology, and minimal to no immune cell infiltration of the spinal cord and no demyelination, similar to or at par with mice that received no EAE injections (negative control). Mice receiving NI111 (NF-κB1 + TNFR1) also showed reduced neuroinflammation compared to saline (sham)-treated EAE mice and at par/similar to other inflammasome-inhibiting small molecule treatments, although it was significantly higher than NI112 leading to subsequent worsening clinical outcomes. Furthermore, treatment with an oral formulation of NI112 at lower doses showed a significant reduction in EAE severity, albeit with higher variance owing to administration and formulation/fill-and-finish variability. Overall, these results point to the potential of further development and testing of these inflammasome-targeting Nanoliogmers as an effective neuroinflammation treatment for multiple neurodegenerative diseases and potentially benefit several patients suffering from such debilitating autoimmune diseases like MS.

Star power: harnessing the reactive astrocyte response to promote remyelination in multiple sclerosis

Astrocytes are indispensable for central nervous system development and homeostasis. In response to injury and disease, astrocytes are integral to the immunological- and the, albeit limited, repair response. In this review, we will examine some of the functions reactive astrocytes play in the context of multiple sclerosis and related animal models. We will consider the heterogeneity or plasticity of astrocytes and the mechanisms by which they promote or mitigate demyelination. Finally, we will discuss a set of biomedical strategies that can stimulate astrocytes in their promyelinating response.

Complement tunes glutamate release and supports synaptic impairments in an animal model of multiple sclerosis

BACKGROUND AND PURPOSE

To deepen our knowledge of the role of complement in synaptic impairment in experimental autoimmune encephalomyelitis (EAE) mice, we investigated the distribution of C1q and C3 proteins and the role of complement as a promoter of glutamate release in purified nerve endings (synaptosomes) and astrocytic processes (gliosomes) isolated from the cortex of EAE mice at the acute stage of the disease (21 ± 1 day post-immunization).

EXPERIMENTAL APPROACH

EAE cortical synaptosomes and gliosomes were analysed for glutamate release efficiency (measured as release of preloaded [3 H]D-aspartate ([3 H]D-ASP)), C1q and C3 protein density, and for viability and ongoing apoptosis.

KEY RESULTS

In healthy mice, complement releases [3 H]D-ASP from gliosomes more efficiently than from synaptosomes. The releasing activity occurs in a dilution-dependent manner and involves the reversal of the excitatory amino acid transporters (EAATs). In EAE mice, the complement-induced releasing activity is significantly reduced in cortical synaptosomes but amplified in cortical gliosomes. These adaptations are paralleled by decreased density of the EAAT2 protein in synaptosomes and increased EAAT1 staining in gliosomes. Concomitantly, PSD95, GFAP, and CD11b, but not SNAP25, proteins are overexpressed in the cortex of the EAE mice. Similarly, C1q and C3 protein immunostaining is increased in EAE cortical synaptosomes and gliosomes, although signs of ongoing apoptosis or altered viability are not detectable.

CONCLUSION AND IMPLICATIONS

Our results unveil a new noncanonical role of complement in the CNS of EAE mice relevant to disease progression and central synaptopathy that suggests new therapeutic targets for the management of MS.

The Role of Complement Dysregulation in Glaucoma

Glaucoma is a progressive neurodegenerative disease characterized by damage to the optic nerve that results in irreversible vision loss. While the exact pathology of glaucoma is not well understood, emerging evidence suggests that dysregulation of the complement system, a key component of innate immunity, plays a crucial role. In glaucoma, dysregulation of the complement cascade and impaired regulation of complement factors contribute to chronic inflammation and neurodegeneration. Complement components such as C1Q, C3, and the membrane attack complex have been implicated in glaucomatous neuroinflammation and retinal ganglion cell death. This review will provide a summary of human and experimental studies that document the dysregulation of the complement system observed in glaucoma patients and animal models of glaucoma driving chronic inflammation and neurodegeneration. Understanding how complement-mediated damage contributes to glaucoma will provide opportunities for new therapies.

Virus-host protein co-expression networks reveal temporal organization and strategies of viral infection

Viral replication is a complex dynamical process involving the global remodeling of the host cellular machinery across several stages. In this study, we provide a unified view of the virus-host interaction at the proteome level reconstructing protein co-expression networks from quantitative temporal data of four large DNA viruses. We take advantage of a formal framework, the theory of competing networks, to describe the viral infection as a dynamical system taking place on a network of networks where perturbations induced by viral proteins spread to hijack the host proteome for the virus benefit. Our methodology demonstrates how the viral replication cycle can be effectively examined as a complex interaction between protein networks, providing useful insights into the viral and host's temporal organization and strategies, key protein nodes targeted by the virus and dynamical bottlenecks during the course of the infection.

The role of C5a receptors in autoimmunity

The complement system is an essential component of the innate immune response and plays a vital role in host defense and inflammation. Dysregulation of the complement system, particularly involving the anaphylatoxin C5a and its receptors (C5aR1 and C5aR2), has been linked to several autoimmune diseases, indicating the potential for targeted therapies. C5aR1 and C5aR2 are seven-transmembrane receptors with distinct signaling mechanisms that play both partially overlapping and opposing roles in immunity. Both receptors are expressed on a broad spectrum of immune and non-immune cells and are involved in cellular functions and physiological processes during homeostasis and inflammation. Dysregulated C5a-mediated inflammation contributes to autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, epidermolysis bullosa acquisita, antiphospholipid syndrome, and others. Therefore, targeting C5a or its receptors may yield therapeutic innovations in these autoimmune diseases by reducing the recruitment and activation of immune cells that lead to tissue inflammation and injury, thereby exacerbating the autoimmune response. Clinical trials focused on the inhibition of C5 cleavage or the C5a/C5aR1-axis using small molecules or monoclonal antibodies hold promise for bringing novel treatments for autoimmune diseases into practice. However, given the heterogeneous nature of (systemic) autoimmune diseases, there are still several challenges, such as patient selection, optimal dosing, and treatment duration, that require further investigation and development to realize the full therapeutic potential of C5a receptor inhibition, ideally in the context of a personalized medicine approach. Here, we aim to provide a brief overview of the current knowledge on the function of C5a receptors, the involvement of C5a receptors in autoimmune disorders, the molecular mechanisms underlying C5a receptor-mediated autoimmunity, and the potential for targeted therapies to modulate their activity.

The anaphylatoxin C5a: Structure, function, signaling, physiology, disease, and therapeutics

The complement system is one of the oldest known tightly regulated host defense systems evolved for efficiently functioning cell-based immune systems and antibodies. Essentially, the complement system acts as a pivot between the innate and adaptive arms of the immune system. The complement system collectively represents a cocktail of ∼50 cell-bound/soluble glycoproteins directly involved in controlling infection and inflammation. Activation of the complement cascade generates complement fragments like C3a, C4a, and C5a as anaphylatoxins. C5a is the most potent proinflammatory anaphylatoxin, which is involved in inflammatory signaling in a myriad of tissues. This review provides a comprehensive overview of human C5a in the context of its structure and signaling under several pathophysiological conditions, including the current and future therapeutic applications targeting C5a.