The mystery behind membrane insertion: a review of the complement membrane attack complex

Aortic aneurysm and dissection: complement and precision medicine in aortic disease

Aortic disease encompasses life-threatening conditions such as aortic aneurysm and dissection, which are associated with high prevalence, morbidity, and mortality. The complement system, a key component of innate immunity, not only defends against pathogens but also maintains tissue homeostasis. Recent discoveries have expanded its role beyond immunity, linking complement dysregulation to numerous diseases and positioning it as a target for pharmacotherapy. Complement-based treatments for precision medicine are emerging, with several pharmaceuticals either already approved or under investigation. In aortic disease, complement activation and dysregulation have unveiled novel mechanisms and clinical implications. Human and experimental studies suggest that all three complement pathways contribute to disease pathophysiology. The complement system induces direct cellular damage via the membrane attack complex, as well as matrix-metalloproteinase (MMP)-associated tissue damage by promoting MMP-2 and MMP-9 expression. The anaphylatoxins C3a and C5a exacerbate disease by recruiting immune cells and triggering proinflammatory responses. Examples include neutrophil extracellular trap formation and cytokine release by polymorphonuclear neutrophils. These findings highlight the complement system as a promising novel diagnostic and therapeutic target in aortic disease with potential for individualized treatment. However, gaps remain, emphasizing the need for standardized multisite preclinical studies to improve reproducibility and translation. Biomarker studies must also be validated across diverse patient cohorts for clinical applicability. This review examines current knowledge regarding complement in aortic disease, aiming to evaluate its potential for innovative diagnostic and personalized treatment strategies.

Functional divergence of CAD-like family genes in Saccharum complex under biotic and abiotic stress

KEY MESSAGE

A total of 54 genes of membrane attack complex/perforin (MACPF) superfamily were identified in Saccharum complex and function divergence among SsaCAD-like genes were present in plant against stressors. The membrane attack complex/perforin (MACPF) superfamily belongs to pore-forming proteins involving in innate and adaptive immunity in eukaryotes. The constitutively activated cell death (CAD) proteins contained the MACPF domain participate in plant defense responses under adverse conditions. However, the characteristics and functions of CAD-like genes in sugarcane are still poorly understood. In this study, 54 CAD-like genes were identified in three genomes from Saccharum complex including two clones (Np-X and AP85-441) of Saccharum spontaneum and a clone (Yunnan2009-3) of Erianthus rufipilus. All CAD-like genes were categorized into five phylogenetic groups (I-V). Various cis-acting elements related to stress responses, such as phytohormone response elements, were found in promoter regions. Transcriptome and RT-qPCR analysis demonstrated these genes possessing diverse expression profiles. The SsaCAD1-like1 gene was upregulated in sugarcane cultivars after cold treatment and infection by Xanthomonas albilineans (Xa) causing leaf scald. Meanwhile, this gene was downregulated under drought and ABA treatments but was upregulated and then downregulated across time-points of SA treatment. The SsaCAD4-like1 gene was downregulated under five abiotic stressors. Expression levels of two alleles (SsaCAD2-like1/2) were significantly decreased under all abiotic stressors except for salinity treatment. Similar expression patterns of three alleles (SsaCAD3-like1/2/4) were found under abiotic stress. The SsaCAD1-like1 exhibited a negative role but SsaCAD3-like2/4 acted as positive roles in transgenic Arabidopsis lines against bacterial pathogen infection. Our results provide novel gene resources for developing disease-resistant cultivars in sugarcane.

Action of the Terminal Complement Pathway on Cell Membranes

The complement pathway is one of the most ancient elements of the host's innate response and includes a set of protein effectors that rapidly react against pathogens. The late stages of the complement reaction are broadly categorised into two major outcomes. Firstly, C5a receptors, expressed on membranes of host cells, are activated by C5a to generate pro-inflammatory responses. Secondly, target cells are lysed by a hetero-oligomeric pore known as the membrane attack complex (MAC) that punctures the cellular membrane, causing ion and osmotic flux. Generally, several membrane-bound and soluble inhibitors protect the host membrane from complement damage. This includes inhibitors against the MAC, such as clusterin and CD59. This review addresses the most recent molecular and structural insights behind the activation and modulation of the integral membrane proteins, the C5a receptors (C5aR1 and C5aR2), as well as the regulation of MAC assembly. The second aspect of the review focuses on the molecular basis behind inflammatory diseases that are reflective of failure to regulate the terminal complement effectors. Although each arm is unique in its function, both pathways may share similar outcomes in these diseases. As such, the review outlines potential synergy and crosstalk between C5a receptor activation and MAC-mediated cellular responses.

Guianensin, a Blackfly Salivary Protein, Inhibits the Lectin Pathway of Complement

Salivary secretions from blood-feeding arthropods are rich in bioactive compounds that counteract blood clotting, platelet aggregation, complement activation, and vasoconstriction. Despite the identification and characterization of various salivary components in blood-feeding arthropods, their role in complement inhibition, particularly in black flies, remains underexplored. Here, we found that Guianensin, a salivary protein from Simulium guianense, is a specific inhibitor of the lectin pathway of the complement. Guianensin targets MASP-2, a serine protease crucial for LP activation resulting in reduced C4 and C5b-9 complex deposition. Guianensin also inhibits the procoagulant activity of MASP-2 in vitro. No interaction with C1s, C1r, or other downstream complement proteins was found. Using a lipopolysaccharide-induced murine lung injury model, Guianensin significantly reduced neutrophil numbers and inflammatory cytokines, demonstrating its strong anti-inflammatory activity in vivo. Guianensin emerges as a novel complement inhibitor and a potential candidate for therapeutic applications.

Large and Stable Nanopores Formed by Complement Component 9 for Characterizing Single Folded Proteins

Biological nanopores offer a promising approach for single-molecule analysis of nucleic acids, peptides, and proteins. The work presented here introduces a biological nanopore formed by the self-assembly of complement component 9 (C9). This exceptionally large and cylindrical protein pore is composed of 20 ± 4 monomers of C9 resulting in a diameter of 10 ± 4 nm and an effective pore length of 13 nm. These poly(C9) pores remain stable for up to 30 min without indications of gating, flickering, or clogging across a range of transmembrane voltages (-150 to +150 mV) and ionic strengths (50 to 1000 mM). At physiologic pH, the ring-shaped distribution of negative and positive surface charges in the lumen of the pore enables capture of analyte proteins by electro-osmotic flow and leads to residence times of analyte proteins whose most probable values can exceed 300 μs. We used poly(C9) nanopores to determine the volume and shape of unlabeled folded proteins with molecular weights between 9 and 230 kDa with unprecedented accuracy in the context of resistive pulse recordings. Finally, poly(C9) pores made it possible to distinguish between the open and closed conformations of adenylate kinase based on differences in current modulations within resistive pulses and the corresponding differences in approximations of their shape. Thus, poly(C9) nanopores enable highly sensitive and accurate characterization of a wide range of natively folded proteins on a single molecule level.

Long COVID: Clinical Findings, Pathology, and Endothelial Molecular Mechanisms

Persistence of COVID-19 symptoms may follow severe acute respiratory syndrome coronavirus 2 infection. The incidence of long COVID increases with the severity of acute disease, but even mild disease can be associated with sequelae. The symptoms vary widely, with fatigue, shortness of breath, and cognitive dysfunction the most common. Abnormalities of multiple organs have been documented, and histopathology has revealed widespread microthrombi. Elevated levels of complement are present in acute COVID-19 patients and may persist at lower levels in long COVID. Evidence supports complement activation, with endotheliopathy-associated disease as the molecular mechanism causing both acute and long COVID.

Hepatocyte nuclear factor 4α is a critical factor for the production of complement components in the liver

The complement system plays an important role in biological defense as an effector to eliminate microorganisms that invade an organism and it is composed of more than 50 proteins, most of which are produced in the liver. Of these proteins, the mRNA expression of C3 and Cfb is known to be positively regulated by the nuclear receptor HNF4α. To investigate whether HNF4α regulates the complement system, we analyzed the hepatic expression of genes involved in the complement activation pathway and membrane attack complex (MAC) formation within the complement system using liver-specific Hnf4a-null mice (Hnf4aΔHep mice) and tamoxifen-induced liver-specific Hnf4a-null mice (Hnf4af/f;AlbERT2cre mice). We found that hepatic expression of many complement genes including C8a, C8b, C8g, and C9 that are involved in formation of the MAC was markedly decreased in Hnf4aΔHep mice and Hnf4af/f;AlbERT2cre mice. Furthermore, expression of C8A, C8B, and C8G was also decreased in human hepatoma cell lines in which the expression of HNF4α was suppressed, and expression of C8G and C9 was induced in a human immortalized hepatocyte cell line with forced expression of HNF4α. Transactivation of C8g and C9 was dependent on HNF4α expression of HNF4α binding sites, indicating that C8g and C9 are novel target genes of HNF4α. The results suggest that hepatic HNF4α plays an important role in regulation of the complement system, mainly MAC formation.

The Prokaryotic Roots of Eukaryotic Immune Systems

Over the past two decades, studies have revealed profound evolutionary connections between prokaryotic and eukaryotic immune systems, challenging the notion of their unrelatedness. Immune systems across the tree of life share an operational framework, shaping their biochemical logic and evolutionary trajectories. The diversification of immune genes in the prokaryotic superkingdoms, followed by lateral transfer to eukaryotes, was central to the emergence of innate immunity in the latter. These include protein domains related to nucleotide second messenger-dependent systems, NAD+/nucleotide degradation, and P-loop NTPase domains of the STAND and GTPase clades playing pivotal roles in eukaryotic immunity and inflammation. Moreover, several domains orchestrating programmed cell death, ultimately of prokaryotic provenance, suggest an intimate link between immunity and the emergence of multicellularity in eukaryotes such as animals. While eukaryotes directly adopted some proteins from bacterial immune systems, they repurposed others for new immune functions from bacterial interorganismal conflict systems. These emerging immune components hold substantial biotechnological potential.

Pre-Clinical Studies of a Novel Bispecific Fusion Protein Targeting C3b and VEGF in Neovascular and Nonexudative AMD Models

INTRODUCTION

KNP-301 is a bi-specific fragment crystallizable region (Fc) fusion protein, which inhibits both C3b and vascular endothelial growth factor (VEGF) simultaneously for patients with late-stage age-related macular degeneration (AMD). The present study evaluated in vitro potency, in vivo efficacy, intravitreal pharmacokinetics (IVT PK), and injectability of KNP-301.

METHODS

C3b and VEGF binding of KNP-301 were assessed by surface plasmon resonance (SPR) and enzyme-linked immunosorbent assay (ELISA), and cellular bioassays. A laser-induced choroidal neovascularization (CNV) model and a sodium iodate-induced nonexudative AMD model were used to test the in vivo efficacy of mouse surrogate of KNP-301. Utilizing fluorescein angiography (FA) and spectral-domain optical coherence tomography (SD-OCT) scans, the reduction in disease lesions were analyzed in a CNV mouse model. In the nonexudative AMD mouse model, outer nuclear layer (ONL) was assessed by immunofluorescence staining. Lastly, intravitreal pharmacokinetic study was conducted with New Zealand white rabbits via IVT administration of KNP-301 and injectability of KNP-301 was examined by a viscosity test at high concentrations.

RESULTS

KNP-301 bound C3b selectively, which resulted in a blockade of the alternative pathway, not the classical pathway. KNP-301 also acted as a VEGF trap, impeding VEGF-mediate signaling. Our dual-blockade strategy was effective in both neovascular and nonexudative AMD models. Moreover, KNP-301 had an advantage of potentially less frequent dosing due to the long half-life in the intravitreal chamber. Our viscosity assessment confirmed that KNP-301 meets the criteria of the IVT injection.

CONCLUSIONS

Unlike current therapies, KNP-301 is expected to cover patients with late-stage AMD of both neovascular and nonexudative AMD, and its long-term PK profile at the intravitreal chamber would allow convenience in the dosing interval of patients.

Identification of Tumor Budding-Associated Genes in Breast Cancer through Transcriptomic Profiling and Network Diffusion Analysis

Breast cancer has the highest diagnosis rate among all cancers. Tumor budding (TB) is recognized as a recent prognostic marker. Identifying genes specific to high-TB samples is crucial for hindering tumor progression and metastasis. In this study, we utilized an RNA sequencing technique, called TempO-Seq, to profile transcriptomic data from breast cancer samples, aiming to identify biomarkers for high-TB cases. Through differential expression analysis and mutual information, we identified seven genes (NOL4, STAR, C8G, NEIL1, SLC46A3, FRMD6, and SCARF2) that are potential biomarkers in breast cancer. To gain more relevant proteins, further investigation based on a protein-protein interaction network and the network diffusion technique revealed enrichment in the Hippo signaling and Wnt signaling pathways, promoting tumor initiation, invasion, and metastasis in several cancer types. In conclusion, these novel genes, recognized as overexpressed in high-TB samples, along with their associated pathways, offer promising therapeutic targets, thus advancing treatment and diagnosis for breast cancer.

CAD1 contributes to osmotic tolerance in Arabidopsis thaliana by suppressing immune responses under osmotic stress

Acquired osmotolerance induced by initial exposure to mild salt stress is widespread across Arabidopsis thaliana ecotypes, but the mechanism underlying it remains poorly understood. To clarify it, we isolated acquired osmotolerance-deficient 1 (aod1), a mutant highly sensitive to osmotic stress, from ion-beam-irradiated seeds of Zu-0, an ecotype known for its remarkably high osmotolerance. Aod1 showed growth inhibition with spotted necrotic lesions on the rosette leaves under normal growth conditions on soil. However, its tolerance to salt and oxidative stresses was similar to that of the wild type (WT). Genetic and genome sequencing analyses suggested that the gene causing aod1 is identical to CONSTITUTIVELY ACTIVATED CELL DEATH 1 (CAD1). Complementation with the WT CAD1 gene restored the growth and osmotolerance of aod1, indicating that mutated CAD1 is responsible for the observed phenotypes in aod1. Although CAD1 is known to act as a negative regulator of immune response, transcript levels in the WT increased in response to osmotic stress. Aod1 displayed enhanced immune response and cell death under normal growth conditions, whereas the expression profiles of osmotic response genes were comparable to those of the WT. These findings suggest that autoimmunity in aod1 is detrimental to osmotolerance. Overall, our results suggest that CAD1 negatively regulates immune responses under osmotic stress, contributing to osmotolerance in Arabidopsis.

Regulatory gene network for coffee-like color morph of TYRP1 mutant of oujiang color common carp

BACKGROUND

Neither a TYRP1-mediated highly conserved genetic network underlying skin color towards optimum defense nor the pathological tendency of its mutation is well understood. The Oujiang Color Common Carp (Cyprinus carpio var. color) as a model organism, offering valuable insights into genetics, coloration, aquaculture practices, and environmental health. Here, we performed a comparative skin transcriptome analysis on TYRP1 mutant and wild fishes by applying a conservative categorical approach considering different color phenotypes.

RESULTS

Our results reveal that an unusual color phenotype may be sensitized with TYRP1 mutation as a result of upregulating several genes related to an anti-inflammatory autoimmune system in response to the COMT-mediated catecholamine neurotransmitters in the skin. Particularly, catecholamines-derived red/brown, red with blue colored membrane attack complex, and brown/grey colored reduced eumelanin are expected to be aggregated in the regenerated cells.

CONCLUSIONS

It is, thus, concluded that the regenerated cells with catecholamines, membrane attack complex, and eumelanin altogether may contribute to the formation of the unusual (coffee-like) color phenotype in TYRP1 mutant.

Cell Membrane Perforation: Patterns, Mechanisms and Functions

Cell membrane is crucial for the cellular activities, and any disruption to it may affect the cells. It is demonstrated that cell membrane perforation is associated with some biological processes like programmed cell death (PCD) and infection of pathogens. Specific developments make it a promising technique to perforate the cell membrane controllably and precisely. The pores on the cell membrane provide direct pathways for the entry and exit of substances, and can also cause cell death, which means reasonable utilization of cell membrane perforation is able to assist intracellular delivery, eliminate diseased or cancerous cells, and bring about other benefits. This review classifies the patterns of cell membrane perforation based on the mechanisms into 1) physical patterns, 2) biological patterns, and 3) chemical patterns, introduces the characterization methods and then summarizes the functions according to the characteristics of reversible and irreversible pores, with the aim of providing a comprehensive summary of the knowledge related to cell membrane perforation and enlightening broad applications in biomedical science.

Genotype-environment associations reveal genes potentially linked to avian malaria infection in populations of an endemic island bird

Patterns of pathogen prevalence are, at least partially, the result of coevolutionary host-pathogen interactions. Thus, exploring the distribution of host genetic variation in relation to infection by a pathogen within and across populations can provide important insights into mechanisms of host defence and adaptation. Here, we use a landscape genomics approach (Bayenv) in conjunction with genome-wide data (ddRADseq) to test for associations between avian malaria (Plasmodium) prevalence and host genetic variation across 13 populations of the island endemic Berthelot's pipit (Anthus berthelotii). Considerable and consistent spatial heterogeneity in malaria prevalence was observed among populations over a period of 15 years. The prevalence of malaria infection was also strongly positively correlated with pox (Avipoxvirus) prevalence. Multiple host loci showed significant associations with malaria prevalence after controlling for genome-wide neutral genetic structure. These sites were located near to or within genes linked to metabolism, stress response, transcriptional regulation, complement activity and the inflammatory response, many previously implicated in vertebrate responses to malarial infection. Our findings identify diverse genes - not just limited to the immune system - that may be involved in host protection against malaria and suggest that spatially variable pathogen pressure may be an important evolutionary driver of genetic divergence among wild animal populations, such as Berthelot's pipit. Furthermore, our data indicate that spatio-temporal variation in multiple different pathogens (e.g. malaria and pox in this case) may have to be studied together to develop a more holistic understanding of host pathogen-mediated evolution.

FVB/NJ strain as a mouse model for cutaneous leishmaniasis by Leishmania (L.) amazonensis

BACKGROUND

Leishmaniases encompass a spectrum of neglected diseases caused by parasites of the genus Leishmania, grouped in two forms: tegumentary and visceral leishmaniasis.

OBJECTIVES

In this study, we propose Friend Virus B NIH Jackson (FVB/NJ) mouse strain as a new experimental model of infection with Leishmania (Leishmania) amazonensis, the second most prevalent agent of tegumentary leishmaniasis in Brazil.

METHODS AND FINDINGS

We performed in vitro infections of FVB/NJ macrophages and compared them with BALB/c macrophages, showing that BALB/c cells have higher infection percentages and a higher number of amastigotes/cell. Phagocytosis assays indicated that BALB/c and FVB/NJ macrophages have similar capacity to uptake parasites after 5 min incubations. We also investigated promastigotes' resistance to sera from FVB/NJ and BALB/c and observed no difference between the two sera, even though FVB/NJ has a deficiency in complement components. Finally, we subcutaneously infected FVB/NJ and BALB/c mice with 2 × 106 parasites expressing luciferase. Analysis of lesion development for 12 weeks showed that FVB/NJ and BALB/c mice have similar lesion profiles and parasite burdens.

MAIN CONCLUSIONS

This work characterises for the first time the FVB/NJ mouse as a new model for tegumentary leishmaniasis caused by Leishmania (L.) amazonensis.

Direct enhancement of viral neutralising antibody potency by the complement system: a largely forgotten phenomenon

Neutralisation assays are commonly used to assess vaccine-induced and naturally acquired immune responses; identify correlates of protection; and inform important decisions on the screening, development, and use of therapeutic antibodies. Neutralisation assays are useful tools that provide the gold standard for measuring the potency of neutralising antibodies, but they are not without limitations. Common methods such as the heat-inactivation of plasma samples prior to neutralisation assays, or the use of anticoagulants such as EDTA for blood collection, can inactivate the complement system. Even in non-heat-inactivated samples, the levels of complement activity can vary between samples. This can significantly impact the conclusions regarding neutralising antibody potency. Restoration of the complement system in these samples can be achieved using an exogenous source of plasma with preserved complement activity or with purified complement proteins. This can significantly enhance the neutralisation titres for some antibodies depending on characteristics such as antibody isotype and the epitope they bind, enable neutralisation with otherwise non-neutralising antibodies, and demonstrate a better relationship between in vitro and in vivo findings. In this review, we discuss the evidence for complement-mediated enhancement of antibody neutralisation against a range of viruses, explore the potential mechanisms which underpin this enhancement, highlight current gaps in the literature, and provide a brief summary of considerations for adopting this approach in future research applications.

Integrated multi-omics approach reveals novel associations in the rapeseed diet-microbiota-host axis in pigs

Diet-mediated host-microbiota interplay is a key factor in optimizing the gut function and overall health of the host. Gaining insight into the biological mechanisms behind this relationship is fundamental to finding sustainable, environment-friendly feed solutions in livestock production systems. Here, we apply a multi-omics integration approach to elucidate sustainable diet-associated host-gut microbiota interactions in pigs and we demonstrate novel and biologically relevant host-microbe associations in the gut, driven by a rapeseed meal-based feed (RSF). Interestingly, RSF-diet promoted the abundance of segmented filamentous bacteria Candidatus Arthromitus that was associated with the maintenance of mucosal immunity in the ileum of pigs. In the colon, RSF diet affected host mRNA splicing functions, which may result in different host gene products, through host-microbiota associations, particularly with the Faecalibacterium population, and through the interaction of dietary components such as sinapic acid with the host cells. Moreover, telomere maintenance and organization functions that may determine the overall health of the host were upregulated and notably associated with Subdoligranulum population in the colon of RSF diet-fed pigs. This integrative multi-omics approach provides more insight into the diet-microbiota-host axis, and a better understanding of mechanisms and opportunities to find new strategies for modulating host health and potentially improving caloric and nutritional efficiency in animal production.

Complement component C1q is an immunological rheostat that regulates Fc:Fc γ R interactions

Though binding sites for the complement factor C1q and the canonical fragment crystallizable (Fc) gamma receptors (Fcγ Rs) on immunoglobulin G (IgG) molecules overlap, how C1q decoration of immune complexes (ICs) influences their ability to engage Fcγ Rs remains unknown. In this report, we use recombinant human Fc multimers as stable IC mimics to show that C1q engagement of ICs directly and transiently inhibits their interactions with Fcγ RIII (CD16) on human natural killer (NK) cells. This inhibition occurs by C1q engagement alone as well as in concert with other serum factors. Furthermore, the inhibition of Fcγ RIII engagement mediated by avid binding of C1q to ICs is directly associated with IC size and dependent on the concentrations of both C1q and Fc multimers present. Functionally, C1q-mediated Fc blockade limits the ability of NK cells to induce the upregulation of the cosignaling molecule, 4-1BB (CD137), and to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). Although C1q is traditionally viewed as a soluble effector molecule, we demonstrate that C1q may also take on the role of an "immunologic rheostat," buffering Fcγ R-mediated activation of immune cells by circulating ICs. These data define a novel role for C1q as a regulator of immune homeostasis and add to our growing understanding that complement factors mediate pleiotropic effects.

Endothelial-derived complement factor D contributes to endothelial dysfunction in malignant nephrosclerosis via local complement activation

Malignant nephrosclerosis is a thrombotic microangiopathy associated with abnormal local activation of the complement alternative pathway (AP). However, the mechanism underlying local AP activation is not fully understood. We hypothesized that complement factor D (CFD) secreted by endothelial cells triggers vascular dysfunction in malignant nephrosclerosis via local complement activation. We investigated the deposition of CFD in human kidney biopsy tissues and the function of endothelial-derived CFD in endothelial cell cultures. Immunofluorescence microscopy and laser microdissection-targeted mass spectrometry revealed significant deposition of CFD in the kidneys of patients with malignant nephrosclerosis. Conditionally immortalized human glomerular endothelial cells (CiGEnCs) continuously expressed and secreted CFD in vitro. CFD knockdown in CiGEnCs by small interfering RNA reduced local complement activation and attenuated the upregulation of intercellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), von Willebrand factor (VWF), and endothelin-1 (ET-1) induced by Ang II. The expression of CFD in CiGEnCs was significantly higher than that in other types of microvascular endothelial cells. Our findings suggest that (i) glomerular endothelial cells are an important source of local renal CFD, (ii) endothelial-derived CFD can activate the local complement system, and (iii) endothelial-derived CFD mediates endothelial dysfunction, which may play a role in the pathogenesis of malignant nephrosclerosis.

Chromogranin B (CHGB) is dimorphic and responsible for dominant anion channels delivered to cell surface via regulated secretion

Regulated secretion is conserved in all eukaryotes. In vertebrates granin family proteins function in all key steps of regulated secretion. Phase separation and amyloid-based storage of proteins and small molecules in secretory granules require ion homeostasis to maintain their steady states, and thus need ion conductances in granule membranes. But granular ion channels are still elusive. Here we show that granule exocytosis in neuroendocrine cells delivers to cell surface dominant anion channels, to which chromogranin B (CHGB) is critical. Biochemical fractionation shows that native CHGB distributes nearly equally in soluble and membrane-bound forms, and both reconstitute highly selective anion channels in membrane. Confocal imaging resolves granular membrane components including proton pumps and CHGB in puncta on the cell surface after stimulated exocytosis. High pressure freezing immuno-EM reveals a major fraction of CHGB at granule membranes in rat pancreatic β-cells. A cryo-EM structure of bCHGB dimer of a nominal 3.5 Å resolution delineates a central pore with end openings, physically sufficient for membrane-spanning and large single channel conductance. Together our data support that CHGB-containing (CHGB+) channels are characteristic of regulated secretion, and function in granule ion homeostasis near the plasma membrane or possibly in other intracellular processes.

Direct Visualization of the Dynamic Process of Epsilon Toxin on Hemolysis

Hemolysis is the process of rupturing erythrocytes (red blood cells) by forming nanopores on their membranes using hemolysins, which then impede membrane permeability. However, the self-assembly process before the state of transmembrane pores and underlying mechanisms of conformational change are not fully understood. In this work, theoretical and experimental evidence of the pre-pore morphology of Clostridium perfringens epsilon toxin (ETX), a typical hemolysin, is provided using in situ atomic force microscopy (AFM) complemented by molecular dynamics (MD) simulations to detect the conformational distribution of different states in Mica. The AFM suggests that the ETX pore is formed in two stages: ETX monomers first attach to the membrane and form a pre-pore in no special conditions required, which then undergo a conformational change to form a transmembrane pore at temperatures above the critical point in the presence of receptors. The authors' MD simulations reveal that initial nucleation occurs when specific amino acids adsorb to negatively charged mica cavities. This work fills the knowledge gap in understanding the early stage of hemolysis and the oligomerization of hemolysins. Moreover, the newly identified pre-pore of ETX holds promise as a candidate for nanopore applications.

Liquid crystalline matrix-induced viscoelastic mechanical stimulation modulates activation and phenotypes of macrophage

Accumulating evidence indicates that the mechanical microenvironment exerts profound influences on inflammation and immune modulation, which are likely to be key factors in successful tissue regeneration. The elastic modulus (Em) of the matrix may be a useful adjustable property to control macrophage activation and the overall inflammatory response. This study constituted a series of Em-tunable liquid crystalline cell model (HpCEs) resembling the viscoelastic characteristic of ECM and explored how mechanical microenvironment induced by liquid crystalline soft matter matrix affected macrophage activation and phenotypes. We have shown that HpCEs prepared in this work exhibited typical cholesteric liquid crystal phase and distinct viscoelastic rheological characteristics. All liquid crystalline HpCE matrices facilitated macrophages growth and maintained cell activity. Macrophages in lower-Em HpCE matrices were more likely to polarize toward the pro-inflammatory M1 phenotype. Conversely, the higher-Em HpCEs induced macrophages into an elongated shape and upregulated M2-related markers. Furthermore, the higher-Em HpCEs (HpCE-O1, HpCE-H2, HpCE-H1) could coax sequential polarization states of RAW264.7 from a classically activated "M1" state toward alternatively activated "M2" state in middle and later stage of cell culture (within 3-7 days in this work), suggesting that the HpCE-based strategies could manipulate the local immune microenvironment and promote the dominance of the pro-inflammatory signals in early stages, while M2 macrophages in later stages. The liquid crystalline soft mode fabricated in this work maybe offer a new design guideline for in vitro cell models and applications.

Surveying membrane landscapes: a new look at the bacterial cell surface

Recent studies applying advanced imaging techniques are changing the way we understand bacterial cell surfaces, bringing new knowledge on everything from single-cell heterogeneity in bacterial populations to their drug sensitivity and mechanisms of antimicrobial resistance. In both Gram-positive and Gram-negative bacteria, the outermost surface of the bacterial cell is being imaged at nanoscale; as a result, topographical maps of bacterial cell surfaces can be constructed, revealing distinct zones and specific features that might uniquely identify each cell in a population. Functionally defined assembly precincts for protein insertion into the membrane have been mapped at nanoscale, and equivalent lipid-assembly precincts are suggested from discrete lipopolysaccharide patches. As we review here, particularly for Gram-negative bacteria, the applications of various modalities of nanoscale imaging are reawakening our curiosity about what is conceptually a 3D cell surface landscape: what it looks like, how it is made and how it provides resilience to respond to environmental impacts.

Anti-inflammatory actions of Pentosan polysulfate sodium in a mouse model of influenza virus A/PR8/34-induced pulmonary inflammation

Introduction

There is an unmet medical need for effective anti-inflammatory agents for the treatment of acute and post-acute lung inflammation caused by respiratory viruses. The semi-synthetic polysaccharide, Pentosan polysulfate sodium (PPS), an inhibitor of NF-kB activation, was investigated for its systemic and local anti-inflammatory effects in a mouse model of influenza virus A/PR8/1934 (PR8 strain) mediated infection.

Methods

Immunocompetent C57BL/6J mice were infected intranasally with a sublethal dose of PR8 and treated subcutaneously with 3 or 6 mg/kg PPS or vehicle. Disease was monitored and tissues were collected at the acute (8 days post-infection; dpi) or post-acute (21 dpi) phase of disease to assess the effect of PPS on PR8-induced pathology.

Results

In the acute phase of PR8 infection, PPS treatment was associated with a reduction in weight loss and improvement in oxygen saturation when compared to vehicle-treated mice. Associated with these clinical improvements, PPS treatment showed a significant retention in the numbers of protective SiglecF+ resident alveolar macrophages, despite uneventful changes in pulmonary leukocyte infiltrates assessed by flow cytometry. PPS treatment in PR8- infected mice showed significant reductions systemically but not locally of the inflammatory molecules, IL-6, IFN-g, TNF-a, IL-12p70 and CCL2. In the post-acute phase of infection, PPS demonstrated a reduction in the pulmonary fibrotic biomarkers, sICAM-1 and complement factor C5b9.

Discussion

The systemic and local anti-inflammatory actions of PPS may regulate acute and post-acute pulmonary inflammation and tissue remodeling mediated by PR8 infection, which warrants further investigation.

Genome-wide screen in human plasma identifies multifaceted complement evasion of Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic Gram-negative pathogen, is a leading cause of bacteremia with a high mortality rate. We recently reported that P. aeruginosa forms a persister-like sub-population of evaders in human plasma. Here, using a gain-of-function transposon sequencing (Tn-seq) screen in plasma, we identified and validated previously unknown factors affecting bacterial persistence in plasma. Among them, we identified a small periplasmic protein, named SrgA, whose expression leads to up to a 100-fold increase in resistance to killing. Additionally, mutants in pur and bio genes displayed higher tolerance and persistence, respectively. Analysis of several steps of the complement cascade and exposure to an outer-membrane-impermeable drug, nisin, suggested that the mutants impede membrane attack complex (MAC) activity per se. Electron microscopy combined with energy-dispersive X-ray spectroscopy (EDX) revealed the formation of polyphosphate (polyP) granules upon incubation in plasma of different size in purD and wild-type strains, implying the bacterial response to a stress signal. Indeed, inactivation of ppk genes encoding polyP-generating enzymes lead to significant elimination of persisting bacteria from plasma. Through this study, we shed light on a complex P. aeruginosa response to the plasma conditions and discovered the multifactorial origin of bacterial resilience to MAC-induced killing.

The neoepitope of the complement C5b-9 Membrane Attack Complex is formed by proximity of adjacent ancillary regions of C9

The Membrane Attack Complex (MAC) is responsible for forming large β-barrel channels in the membranes of pathogens, such as gram-negative bacteria. Off-target MAC assembly on endogenous tissue is associated with inflammatory diseases and cancer. Accordingly, a human C5b-9 specific antibody, aE11, has been developed that detects a neoepitope exposed in C9 when it is incorporated into the C5b-9 complex, but not present in the plasma native C9. For nearly four decades aE11 has been routinely used to study complement, MAC-related inflammation, and pathophysiology. However, the identity of C9 neoepitope remains unknown. Here, we determined the cryo-EM structure of aE11 in complex with polyC9 at 3.2 Å resolution. The aE11 binding site is formed by two separate surfaces of the oligomeric C9 periphery and is therefore a discontinuous quaternary epitope. These surfaces are contributed by portions of the adjacent TSP1, LDLRA, and MACPF domains of two neighbouring C9 protomers. By substituting key antibody interacting residues to the murine orthologue, we validated the unusual binding modality of aE11. Furthermore, aE11 can recognise a partial epitope in purified monomeric C9 in vitro, albeit weakly. Taken together, our results reveal the structural basis for MAC recognition by aE11.

Alterations in ileal transcriptomics during an intestinal barrier challenge in lactating Holstein cows fed a Saccharomyces cerevisiae fermentation product identify potential regulatory processes

Stressors such as lack of access to feed, hot temperatures, transportation, and pen changes can cause impairment of ruminal and intestinal barrier function, also known as "leaky gut". Despite the known benefits of some nutritional approaches during periods of stress, little is understood regarding the underlying mechanisms, especially in dairy cows. We evaluated the effect of feeding a Saccharomyces cerevisiae fermentation product (SCFP; NutriTek, Diamond V, Cedar Rapids, IA) on the ileal transcriptome in response to feed restriction (FR), an established model to induce intestinal barrier dysfunction. Multiparous cows [97.1 ± 7.6 days in milk (DIM); n = 5/group] fed a control diet or control plus 19 g/d SCFP for 9 wk were subjected to an FR challenge for 5 d during which they were fed 40% of their ad libitum intake from the 7 d before FR. All cows were slaughtered at the end of FR, and ileal scrapping RNA was used for RNAseq (NovaSeq 6000, 100 bp read length). Statistical analysis was performed in R and bioinformatics using the KEGG (Kyoto Encyclopedia of Genes and Genomes) and GO databases. One thousand six hundred and ninety-six differentially expressed genes (DEG; FDR-adjusted P ≤ 0.10) were detected in SCFP vs. control, with 451 upregulated and 1,245 downregulated. "Mucin type O-glycan biosynthesis" was the top downregulated KEGG pathway due to downregulation of genes catalyzing glycosylation of mucins (GCNT3, GALNT5, B3GNT3, GALNT18, and GALNT14). An overall downregulation of cell and tissue structure genes (e.g., extracellular matrix proteins) associated with collagen (COL6A1, COL1A1, COL4A1, COL1A2, and COL6A2), laminin (LAMB2), and integrins (ITGA8, ITGA2, and ITGA5) also were detected with SCFP. A subset of DEG enriched in the GO term "extracellular exosome" and "extracellular space". Chemokines within "Cytokine-cytokine receptor interaction pathways" such as CCL16, CCL21, CCL14, CXCL12, and CXCL14 were downregulated by SCFP. The "Glutathione metabolism" pathway was upregulated by SCFP, including GSTA1 and RRM2B among the top upregulated genes, and GSTM1 and GPX8 as top downregulated genes. There were 9 homeobox transcription factors among the top 50 predicted transcription factors using the RNAseq DEG dataset, underscoring the importance of cell differentiation as a potential target of dietary SCFP. Taken together, SCFP downregulated immune-, ECM-, and mucin synthesis-related genes during FR. Homeobox transcription factors appear important for the transcriptional response of SCFP.

The Many Faces of Hemolysis

Hemolysis is a problem associated with a variety of red cell pathologies and physiologies not limited to the transfusion of cells. Various pathways lead to the observed outcomes when a hemolytic event occurs. Each event, and the pathway it follows, is based on characteristics of the red cell, the location in which the hemolysis occurs, and the interaction of the immune system. The severity of an event can be predicted with the knowledge of how these 3 factors interface. Although not all hemolytic events are alike, similarities may exist when the pathways overlap.

Evidence of Chronic Complement Activation in Asymptomatic Pediatric Brain Injury Patients: A Pilot Study

Physical insult from a mild Traumatic Brain Injury (mTBI) leads to changes in blood flow in the brain and measurable changes in white matter, suggesting a physiological basis for chronic symptom presentation. Post-traumatic headache (PTH) is frequently reported by persons after an mTBI that may persist beyond the acute period (>3 months). It remains unclear whether ongoing inflammation may contribute to the clinical trajectory of PTH. We recruited a cohort of pediatric subjects with PTH who had an acute or a persistent clinical trajectory, each around the 3-month post-injury time point, as well as a group of age and sex-matched healthy controls. We collected salivary markers of mRNA expression as well as brain imaging and psychological testing. The persistent PTH group showed the highest levels of psychological burden and pain symptom reporting. Our data suggest that the acute and persistent PTH cohort had elevated levels of complement factors relative to healthy controls. The greatest change in mRNA expression was found in the acute-PTH cohort wherein the complement cascade and markers of vascular health showed a prominent role for C1Q in PTH pathophysiology. These findings (1) underscore a prolonged engagement of what is normally a healthy response and (2) show that a persistent PTH symptom trajectory may parallel a poorly regulated inflammatory response.

The Effect of Remifentanil, MgSO4, or Remifentanil-MgSO4 as Neuroprotectors on BDNF, MAC, and Caspase-3 Levels in Wistar Rats with Traumatic Brain Injury

BACKGROUND: Traumatic brain injury (TBI) can lead to cell death and neurologic dysfunction. Meanwhile, Remifentanyl is an opioid with potent analgesia, while magnesium sulfate (MgSO4) has antinociceptive properties that can prevent hemodynamic instability during laryngoscopy. AIM: This study aims to examine the effect of remifentanil, MgSO4 and their combination on BDNF, MAC, and Caspase-3 levels in Wistar rat models with TBI. METHODOLOGY: An experimental study was conducted on 30 male Wistar rats which were randomly divided into five groups. The control group (G1) received normal saline, the induced group (G2) received normal saline after TBI induction using the modified Feeney method, and the treated group (G3, G4, and G5) received remifentanil, MgSO4, and their combination after TBI induction. The rats’ brain tissues were analyzed for BDNF, MAC, and Caspase-3 levels using ELISA. The data were analyzed statistically with ANOVA followed by post hoc Multiple Comparison Test (p < 0.05). RESULTS: Treatment with remifentanil, MgSO4 or the combination of both in TBI subjects reduced MAC and Caspase-3 but increased the BDNF level. The post hoc multiple comparisons showed significant differences in all groups except groups 3 and 5 in terms of MAC (p = 0.190) and Caspase-3 (p = 0.999). The combination of remifentanil-MgSO4 increased BDNF levels significantly. CONCLUSION: The administration of remifentanil, MgSO4 , or their combination can serve as a neuroprotector in Wistar rat models with TBI by lowering MAC and Caspase-3 as well as increasing BDNF levels.

IL-1β-dependent extravasation of preexisting lung-restricted autoantibodies during lung transplantation activates complement and mediates primary graft dysfunction

Preexisting lung-restricted autoantibodies (LRAs) are associated with a higher incidence of primary graft dysfunction (PGD), although it remains unclear whether LRAs can drive its pathogenesis. In syngeneic murine left lung transplant recipients, preexisting LRAs worsened graft dysfunction, which was evident by impaired gas exchange, increased pulmonary edema, and activation of damage-associated pathways in lung epithelial cells. LRA-mediated injury was distinct from ischemia-reperfusion injury since deletion of donor nonclassical monocytes and host neutrophils could not prevent graft dysfunction in LRA-pretreated recipients. Whole LRA IgG molecules were necessary for lung injury, which was mediated by the classical and alternative complement pathways and reversed by complement inhibition. However, deletion of Fc receptors in donor macrophages or mannose-binding lectin in recipient mice failed to rescue lung function. LRA-mediated injury was localized to the transplanted lung and dependent on IL-1β-mediated permeabilization of pulmonary vascular endothelium, which allowed extravasation of antibodies. Genetic deletion or pharmacological inhibition of IL-1R in the donor lungs prevented LRA-induced graft injury. In humans, preexisting LRAs were an independent risk factor for severe PGD and could be treated with plasmapheresis and complement blockade. We conclude that preexisting LRAs can compound ischemia-reperfusion injury to worsen PGD for which complement inhibition may be effective.

Proteomics and bioinformatics analysis of follicular fluid from patients with polycystic ovary syndrome

Objectives: Polycystic ovary syndrome (PCOS) is a common endocrine and metabolic disorder with heterogeneous manifestations and complex etiology. We used quantitative proteomics analysis based on mass spectrometry to identify the differences in proteomics profiles for follicular fluid obtained from patients with or without PCOS and explore possible mechanisms underlying PCOS.

Methods: Follicular fluid samples were collected from infertile patients with (n = 9) or without (n = 9) PCOS. Total protein was extracted, quantitatively labeled with a tandem mass tag (TMT), and analyzed using liquid chromatography-mass spectrometry (LC‐MS). TMT-based proteomics and bioinformatics analysis were used to determine the differentially expressed proteins (DEPs) and understand the protein networks. The analysis included protein annotation, unsupervised hierarchical clustering, functional classification, functional enrichment and clustering, and protein-protein interaction analysis. Selected DEPs were confirmed by ELISA, and correlation analysis was performed between these DEPs and the clinical characteristics.

Results: In this study, we have identified 1,216 proteins, including 70 DEPs (32 upregulated proteins, 38 downregulated proteins). Bioinformatics analysis revealed that the inflammatory response, complement and coagulation cascades, activation of the immune response, lipid transport, and regulation of protein metabolic processes were co-enriched in patients with PCOS. Based on ELISA results, insulin-like growth factor binding protein 1 (IGFBP1) and apolipoprotein C2 (APOC2) were differentially expressed between patients with and without PCOS. Follicular IGFBP1 showed a positive correlation with the serum levels of high-density lipoprotein cholesterol (HDL-C) (r = 0.3046, p = 0.0419), but negatively correlated with the serum levels of anti-Müllerian hormone (AMH) (r = –0.2924, p = 0.0354) and triglycerides (r = –0.3177, p = 0.0246). Follicular APOC2 was negatively correlated with the serum apolipoprotein A1 (APOA1) levels (r = 0.4509, p = 0.0002).

Conclusion: Our study identified DEPs in the follicular fluid of patients with PCOS. Inflammatory response, complement and coagulation cascades, activation of the immune response, lipid transport, and regulation of protein metabolic process were deregulated in PCOS, which may play essential roles in the pathogenesis of PCOS.

Soluble MAC is primarily released from MAC-resistant bacteria that potently convert complement component C5

The membrane attack complex (MAC or C5b-9) is an important effector of the immune system to kill invading microbes. MAC formation is initiated when complement enzymes on the bacterial surface convert complement component C5 into C5b. Although the MAC is a membrane-inserted complex, soluble forms of MAC (sMAC), or terminal complement complex (TCC), are often detected in sera of patients suffering from infections. Consequently, sMAC has been proposed as a biomarker, but it remains unclear when and how it is formed during infections. Here, we studied mechanisms of MAC formation on different Gram-negative and Gram-positive bacteria and found that sMAC is primarily formed in human serum by bacteria resistant to MAC-dependent killing. Surprisingly, C5 was converted into C5b more potently by MAC-resistant compared to MAC-sensitive Escherichia coli strains. In addition, we found that MAC precursors are released from the surface of MAC-resistant bacteria during MAC assembly. Although release of MAC precursors from bacteria induced lysis of bystander human erythrocytes, serum regulators vitronectin (Vn) and clusterin (Clu) can prevent this. Combining size exclusion chromatography with mass spectrometry profiling, we show that sMAC released from bacteria in serum is a heterogeneous mixture of complexes composed of C5b-8, up to three copies of C9 and multiple copies of Vn and Clu. Altogether, our data provide molecular insight into how sMAC is generated during bacterial infections. This fundamental knowledge could form the basis for exploring the use of sMAC as biomarker.

Overexpression of the Arabidopsis MACPF Protein AtMACP2 Promotes Pathogen Resistance by Activating SA Signaling

Immune response in plants is tightly regulated by the coordination of the cell surface and intracellular receptors. In animals, the membrane attack complex/perforin-like (MACPF) protein superfamily creates oligomeric pore structures on the cell surface during pathogen infection. However, the function and molecular mechanism of MACPF proteins in plant pathogen responses remain largely unclear. In this study, we identified an Arabidopsis MACP2 and investigated the responsiveness of this protein during both bacterial and fungal pathogens. We suggest that MACP2 induces programmed cell death, bacterial pathogen resistance, and necrotrophic fungal pathogen sensitivity by activating the biosynthesis of tryptophan-derived indole glucosinolates and the salicylic acid signaling pathway dependent on the activity of enhanced disease susceptibility 1 (EDS1). Moreover, the response of MACP2 mRNA isoforms upon pathogen attack is differentially regulated by a posttranscriptional mechanism: alternative splicing. In comparison to previously reported MACPFs in Arabidopsis, MACP2 shares a redundant but nonoverlapping role in plant immunity. Thus, our findings provide novel insights and genetic tools for the MACPF family in maintaining SA accumulation in response to pathogens in Arabidopsis.

Structure-Guided Engineering of a Complement Component C3-Binding Nanobody Improves Specificity and Adds Cofactor Activity

The complement system is a part of the innate immune system, where it labels intruding pathogens as well as dying host cells for clearance. If complement regulation is compromised, the system may contribute to pathogenesis. The proteolytic fragment C3b of complement component C3, is the pivot point of the complement system and provides a scaffold for the assembly of the alternative pathway C3 convertase that greatly amplifies the initial complement activation. This makes C3b an attractive therapeutic target. We previously described a nanobody, hC3Nb1 binding to C3 and its degradation products. Here we show, that extending the N-terminus of hC3Nb1 by a Glu-Trp-Glu motif renders the resulting EWE-hC3Nb1 (EWE) nanobody specific for C3 degradation products. By fusing EWE to N-terminal CCP domains from complement Factor H (FH), we generated the fusion proteins EWEnH and EWEµH. In contrast to EWE, these fusion proteins supported Factor I (FI)-mediated cleavage of human and rat C3b. The EWE, EWEµH, and EWEnH proteins bound C3b and iC3b with low nanomolar dissociation constants and exerted strong inhibition of alternative pathway-mediated deposition of complement. Interestingly, EWEnH remained soluble above 20 mg/mL. Combined with the observed reactivity with both human and rat C3b as well as the ability to support FI-mediated cleavage of C3b, this features EWEnH as a promising candidate for in vivo studies in rodent models of complement driven pathogenesis.

Novel Magnetic Elastic Phase-Change Nanodroplets as Dual Mode Contrast Agent for Ultrasound and Magnetic Resonance Imaging

Recently, dual-mode imaging systems merging magnetic resonance imaging (MRI) and ultrasound (US) have been developed. Designing a dual-mode contrast agent is complex due to different mechanisms of enhancement. Herein, we describe novel phase change nanodroplets (PCNDs) with perfluoropentane encapsulated in a pre-polyglycerol sebacate (pre-PGS) shell loaded with polyethylene glycol (PEG)-coated iron oxide nanoparticles as having a dual-mode contrast agent effect. Iron oxide nanoparticles were prepared via the chemical co-precipitation method and PCNDs were prepared via the solvent displacement technique. PCNDs showed excellent enhancement in the in vitro US much more than Sonovue^® microbubbles. Furthermore, they caused a susceptibility effect resulting in a reduction of signal intensity on MRI. An increase in the concentration of nanoparticles caused an increase in the MR contrast effect but a reduction in US intensity. The concentration of nanoparticles in a shell of PCNDs was optimized to obtain a dual-mode contrast effect. Biocompatibility, hemocompatibility, and immunogenicity assays showed that PCNDs were safe and non-immunogenic. Another finding was the dual-mode potential of unloaded PCNDs as T1 MR and US contrast agents. Results suggest the excellent potential of these PCNDs for use as dual-mode contrast agents for both MRI and US.

Cd59 and inflammation regulate Schwann cell development

Efficient neurotransmission is essential for organism survival and is enhanced by myelination. However, the genes that regulate myelin and myelinating glial cell development have not been fully characterized. Data from our lab and others demonstrates that cd59, which encodes for a small GPI-anchored glycoprotein, is highly expressed in developing zebrafish, rodent, and human oligodendrocytes (OLs) and Schwann cells (SCs), and that patients with CD59 dysfunction develop neurological dysfunction during early childhood. Yet, the function of Cd59 in the developing nervous system is currently undefined. In this study, we demonstrate that cd59 is expressed in a subset of developing SCs. Using cd59 mutant zebrafish, we show that developing SCs proliferate excessively and nerves may have reduced myelin volume, altered myelin ultrastructure, and perturbed node of Ranvier assembly. Finally, we demonstrate that complement activity is elevated in cd59 mutants and that inhibiting inflammation restores SC proliferation, myelin volume, and nodes of Ranvier to wildtype levels. Together, this work identifies Cd59 and developmental inflammation as key players in myelinating glial cell development, highlighting the collaboration between glia and the innate immune system to ensure normal neural development.

Development and Optimization of Bifunctional Fusion Proteins to Locally Modulate Complement Activation in Diseased Tissue

Sustained complement activation is an underlying pathologic driver in many inflammatory and autoimmune diseases. Currently approved anti-complement therapies are directed at the systemic blockade of complement. Consequently, these therapies provide widespread inhibition of complement pathway activity, beyond the site of ongoing activation and the intended pharmacodynamic (PD) effects. Given the essential role for complement in both innate and adaptive immunity, there is a need for therapies that inhibit complement in diseased tissue while limiting systemic blockade. One potential approach focuses on the development of novel fusion proteins that enable tissue-targeted delivery of complement negative regulatory proteins. These therapies are expected to provide increased potency and prolonged tissue PD, decreased dosing frequency, and the potential for improved safety profiles. We created a library of bifunctional fusion proteins that direct a fragment of the complement negative regulator, complement receptor type 1 (CR1) to sites of tissue injury. Tissue targeting is accomplished through the binding of the fusion protein to complement C3 fragments that contain a surface-exposed C3d domain and which are covalently deposited on tissues where complement is being activated. To that end, we generated a fusion protein that contains an anti-C3d monoclonal antibody recombinantly linked to the first 10 consensus repeats of CR1 (CR11-10) with the intention of delivering high local concentrations of this complement negative regulatory domain to tissue-bound complement C3 fragments iC3b, C3dg and C3d. Biochemical and in vitro characterization identified several fusion proteins that inhibit complement while maintaining the C3d domain binding properties of the parent monoclonal antibody. Preclinical in vivo studies further demonstrate that anti-C3d fusion proteins effectively distribute to injured tissue and reduce C3 fragment deposition for periods beyond 14 days. The in vitro and in vivo profiles support the further evaluation of C3d mAb-CR11-10 as a novel approach to restore proper complement activation in diseased tissue in the absence of continuous systemic complement blockade.

First-in-human study with ACT-1014-6470, a novel oral complement factor 5a receptor 1 (C5aR1) antagonist, supported by pharmacokinetic predictions from animals to patients

Aberrantly controlled activation of the complement system contributes to inflammatory diseases. Safety, tolerability, and pharmacokinetics of single-ascending doses of ACT-1014-6470, a novel orally available complement factor 5a receptor 1 antagonist, were assessed in a randomized, double-blind, placebo-controlled Phase 1 study. Six ACT-1014-6470 doses (0.5-200 mg) were selected after predictions from a Complex Dedrick plot. In each group, ACT-1014-6470 or matching placebo was administered to six and two healthy male individuals under fed conditions, respectively, including a cross-over part with 10 mg administered also under fasted conditions. Pharmacokinetic blood sampling and safety assessments (adverse events, clinical laboratory, vital signs, 12-lead electrocardiogram, and QT telemetry) were performed. ACT-1014-6470 was absorbed with a time to maximum plasma concentration (t_max ) of 3 h across dose levels and eliminated with a terminal half-life of 30-46 h at doses ≥ 2.5 mg. Exposure increased approximately dose proportionally. Under fed compared to fasted conditions, ACT-1014-6470 exposure was 2.2-fold higher and t_max delayed by 1.5 h. Pharmacokinetic modelling predicted that twice-daily oral administration is warranted in a subsequent multiple-dose study. No clinically relevant findings were observed in safety assessments. ACT-1014-6470 was well tolerated at all doses and could provide a novel therapy with more patient-friendly administration route compared to biologicals.

Development, Characterization, and in vivo Validation of a Humanized C6 Monoclonal Antibody that Inhibits the Membrane Attack Complex

Damage and disease of nerves activates the complement system. We demonstrated that activation of the terminal pathway of the complement system leads to the formation of the membrane attack complex (MAC) and delays regeneration in the peripheral nervous system. Animals deficient in the complement component C6 showed improved recovery after neuronal trauma. Thus, inhibitors of the MAC might be of therapeutic use in neurological disease. Here, we describe the development, structure, mode of action, and properties of a novel therapeutic monoclonal antibody, CP010, against C6 that prevents formation of the MAC in vivo. The monoclonal antibody is humanized and specific for C6 and binds to an epitope in the FIM1-2 domain of human and primate C6 with sub-nanomolar affinity. Using biophysical and structural studies, we show that the anti-C6 antibody prevents the interaction between C6 and C5/C5b by blocking the C6 FIM1-2:C5 C345c axis. Systemic administration of the anti-C6 mAb caused complete depletion of free C6 in circulation in transgenic rats expressing human C6 and thereby inhibited MAC formation. The antibody prevented disease in experimental autoimmune myasthenia gravis and ameliorated relapse in chronic relapsing experimental autoimmune encephalomyelitis in human C6 transgenic rats. CP010 is a promising complement C6 inhibitor that prevents MAC formation. Systemic administration of this C6 monoclonal antibody has therapeutic potential in the treatment of neuronal disease.

Pathophysiological Mechanisms and Treatment of Dermatomyositis and Immune Mediated Necrotizing Myopathies: A Focused Review

Idiopathic inflammatory myopathies (IIM), collectively known as myositis, are a composite group of rare autoimmune diseases affecting mostly skeletal muscle, although other organs or tissues may also be involved. The main clinical feature of myositis is subacute, progressive, symmetrical muscle weakness in the proximal arms and legs, whereas subtypes of myositis may also present with extramuscular features, such as skin involvement, arthritis or interstitial lung disease (ILD). Established subgroups of IIM include dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASyS), overlap myositis (OM) and inclusion body myositis (IBM). Although these subgroups have overlapping clinical features, the widespread variation in the clinical manifestations of IIM suggests different pathophysiological mechanisms. Various components of the immune system are known to be important immunopathogenic pathways in IIM, although the exact pathophysiological mechanisms causing the muscle damage remain unknown. Current treatment, which consists of glucocorticoids and other immunosuppressive or immunomodulating agents, often fails to achieve a sustained beneficial response and is associated with various adverse effects. New therapeutic targets have been identified that may improve outcomes in patients with IIM. A better understanding of the overlapping and diverging pathophysiological mechanisms of the major subgroups of myositis is needed to optimize treatment. The aim of this review is to report on recent advancements regarding DM and IMNM.

Interconnections between Inflammageing and Immunosenescence during Ageing

Acute inflammation is a physiological response to injury or infection, with a cascade of steps that ultimately lead to the recruitment of immune cells to clear invading pathogens and heal wounds. However, chronic inflammation arising from the continued presence of the initial trigger, or the dysfunction of signalling and/or effector pathways, is harmful to health. While successful ageing in older adults, including centenarians, is associated with low levels of inflammation, elevated inflammation increases the risk of poor health and death. Hence inflammation has been described as one of seven pillars of ageing. Age-associated sterile, chronic, and low-grade inflammation is commonly termed inflammageing-it is not simply a consequence of increasing chronological age, but is also a marker of biological ageing, multimorbidity, and mortality risk. While inflammageing was initially thought to be caused by "continuous antigenic load and stress", reports from the last two decades describe a much more complex phenomenon also involving cellular senescence and the ageing of the immune system. In this review, we explore some of the main sources and consequences of inflammageing in the context of immunosenescence and highlight potential interventions. In particular, we assess the contribution of cellular senescence to age-associated inflammation, identify patterns of pro- and anti-inflammatory markers characteristic of inflammageing, describe alterations in the ageing immune system that lead to elevated inflammation, and finally assess the ways that diet, exercise, and pharmacological interventions can reduce inflammageing and thus, improve later life health.

Anti-PEG antibodies compromise the integrity of PEGylated lipid-based nanoparticles via complement

PEGylation of lipid-based nanoparticles and other nanocarriers is widely used to increase their stability and plasma half-life. However, either pre-existing or de novo formed anti-PEG antibodies can induce hypersensitivity reactions and accelerated blood clearance through binding to the nanoparticle surfaces, leading to activation of the complement system. In this study, we investigated the consequences and mechanisms of complement activation by anti-PEG antibodies interacting with different types of PEGylated lipid-based nanoparticles. By using both liposomes loaded with different (model) drugs and LNPs loaded with mRNA, we demonstrate that complement activation triggered by anti-PEG antibodies can compromise the bilayer/surface integrity, leading to premature drug release or exposure of their mRNA contents to serum proteins. Anti-PEG antibodies also can induce deposition of complement fragments onto the surface of PEGylated lipid-based nanoparticles and induce the release of fluid phase complement activation products. The role of the different complement pathways activated by lipid-based nanoparticles was studied using deficient sera and/or inhibitory antibodies. We identified a major role for the classical complement pathway in the early activation events leading to the activation of C3. Our data also confirm the essential role of amplification of C3 activation by alternative pathway components in the lysis of liposomes. Finally, the levels of pre-existing anti-PEG IgM antibodies in plasma of healthy donors correlated with the degree of complement activation (fixation and lysis) induced upon exposure to PEGylated liposomes and mRNA-LNPs. Taken together, anti-PEG antibodies trigger complement activation by PEGylated lipid-based nanoparticles, which can potentially compromise their integrity, leading to premature drug release or cargo exposure to serum proteins.

Molecular mechanisms of vasculopathy and coagulopathy in COVID-19

COVID-19 primarily affects the respiratory system and may lead to severe systemic complications, such as acute respiratory distress syndrome (ARDS), multiple organ failure, cytokine storm, and thromboembolic events. Depending on the immune status of the affected individual early disease control can be reached by a robust type-I-interferon (type-I-IFN) response restricting viral replication. If type-I-IFN upregulation is impaired, patients develop severe COVID-19 that involves profound alveolitis, endothelitis, complement activation, recruitment of immune cells, as well as immunothrombosis. In patients with proper initial disease control there can be a second flare of type-I-IFN release leading to post-COVID manifestation such as chilblain-like lesions that are characterized by thrombosis of small vessels in addition to an inflammatory infiltrate resembling lupus erythematosus (LE). Mechanistically, SARS-CoV-2 invades pneumocytes and endothelial cells by acting on angiotensin-II-converting enzyme 2 (ACE2). It is hypothesized, that viral uptake might downregulate ACE2 bioavailability and enhance angiotensin-II-derived pro-inflammatory and pro-thrombotic state. Since ACE2 is encoded on the X chromosome these conditions might also be influenced by gender-specific regulation. Taken together, SARS-CoV-2 infection affects the vascular compartment leading to variable thrombogenic or inflammatory response depending on the individual immune response status.

Cytokine and Complement Response in the Glaucomatous βB1-CTGF Mouse Model

Glaucoma is a complex neurodegenerative disease leading to a loss of retinal ganglion cells (RGCs) and optic nerve axons. An activation of the complement system seems to contribute to cell loss in this disease. Hence, we investigated a possible initiation of the complement system and the cytokine response in the βB1-CTGF glaucoma model. In these mice, intraocular pressure is elevated, which is the main glaucoma risk factor in patients, and RGC loss occurs at 15 weeks of age. Therefore, quantitative real-time PCR and immunohistological experiments were performed in 5-, 10-, and 15-week-old βB1-CTGF animals and their corresponding wildtypes (WT) to analyze the expression of several complement system factors. We could show that mRNA levels of the terminal complement pathway components C3 and C5 (Hc) were upregulated at 10 weeks. In accordance, more C3+ and membrane attack complex+ cells were observed in transgenic retinae. Further, the C5a receptor anaphylatoxin receptor (C5ar) and the complement component C5a receptor 1 (C5ar1; CD88) mRNA levels were upregulated in 10- and 15-week-old βB1-CTGF mice. Interestingly, all three activation routes of the complement system were elevated in βB1-CTGF mice at some age. Especially C1q, as a marker of the classical pathway, was significantly increased at all investigated ages. Furthermore, mRNA expression levels of interferon-γ (Infg) were upregulated at 5 weeks, while Cxcl1 and Cxcl2 mRNA levels were upregulated at 10 and 15 weeks. The mRNA levels of the chemokines Cxcl10 were increased at all ages in βB1-CTGF mice. These results lead to the assumption that in these transgenic mice, a complement activation mainly through the classical pathway as well as a cytokine response plays a major role in cell death.

Polymerization of C9 enhances bacterial cell envelope damage and killing by membrane attack complex pores

Complement proteins can form membrane attack complex (MAC) pores that directly kill Gram-negative bacteria. MAC pores assemble by stepwise binding of C5b, C6, C7, C8 and finally C9, which can polymerize into a transmembrane ring of up to 18 C9 monomers. It is still unclear if the assembly of a polymeric-C9 ring is necessary to sufficiently damage the bacterial cell envelope to kill bacteria. In this paper, polymerization of C9 was prevented without affecting binding of C9 to C5b-8, by locking the first transmembrane helix domain of C9. Using this system, we show that polymerization of C9 strongly enhanced damage to both the bacterial outer and inner membrane, resulting in more rapid killing of several Escherichia coli and Klebsiella strains in serum. By comparing binding of wildtype and ‘locked’ C9 by flow cytometry, we also show that polymerization of C9 is impaired when the amount of available C9 per C5b-8 is limited. This suggests that an excess of C9 is required to efficiently form polymeric-C9. Finally, we show that polymerization of C9 was impaired on complement-resistant E. coli strains that survive killing by MAC pores. This suggests that these bacteria can specifically block polymerization of C9. All tested complement-resistant E. coli expressed LPS O-antigen (O-Ag), compared to only one out of four complement-sensitive E. coli. By restoring O-Ag expression in an O-Ag negative strain, we show that the O-Ag impairs polymerization of C9 and results in complement-resistance. Altogether, these insights are important to understand how MAC pores kill bacteria and how bacterial pathogens can resist MAC-dependent killing.

In this paper, we focus on how complement proteins, an essential part of the immune system, kill Gram-negative bacteria via so-called membrane attack complex (MAC) pores. The MAC is a large pore that consists of five different proteins. The final component, C9, assembles a ring of up to 18 C9 molecules that damages the bacterial cell envelope. Here, we aimed to better understand if this polymeric-C9 ring is necessary to kill bacteria and if bacteria can interfere in its assembly. We uncover that polymerization of C9 increased the damage to the entire bacterial cell envelope, which resulted in more rapid killing of several Gram-negative species. We also show that some clinical Escherichia coli strains can block polymerization of C9 and survive MAC-dependent killing by modifying sugars in the bacterial cell envelope, namely the O-antigen of lipopolysaccharide. These insights help us to better understand how the immune system kills bacteria and how pathogenic bacteria can survive killing.

The Contribution of Complement to the Pathogenesis of IgA Nephropathy: Are Complement-Targeted Therapies Moving from Rare Disorders to More Common Diseases?

Primary IgA nephropathy (IgAN) is a leading cause of chronic kidney disease and kidney failure for which there is no disease-specific treatment. However, this could change, since novel therapeutic approaches are currently being assessed in clinical trials, including complement-targeting therapies. An improved understanding of the role of the lectin and the alternative pathway of complement in the pathophysiology of IgAN has led to the development of these treatment strategies. Recently, in a phase 2 trial, treatment with a blocking antibody against mannose-binding protein-associated serine protease 2 (MASP-2, a crucial enzyme of the lectin pathway) was suggested to have a potential benefit for IgAN. Now in a phase 3 study, this MASP-2 inhibitor for the treatment of IgAN could mark the start of a new era of complement therapeutics where common diseases can be treated with these drugs. The clinical development of complement inhibitors requires a better understanding by physicians of the biology of complement, the pathogenic role of complement in IgAN, and complement-targeted therapies. The purpose of this review is to provide an overview of the role of complement in IgAN, including the recent discovery of new mechanisms of complement activation and opportunities for complement inhibitors as the treatment of IgAN.

The role of the immune system in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder where the accumulation of amyloid plaques and the formation of tau tangles are the prominent pathological hallmarks. Increasing preclinical and clinical studies have revealed that different components of the immune system may act as important contributors to AD etiology and pathogenesis. The recognition of misfolded Aβ and tau by immune cells can trigger a series of complex immune responses in AD, and then lead to neuroinflammation and neurodegeneration. In parallel, genome-wide association studies have also identified several immune related loci associated with increased - risk of AD by interfering with the function of immune cells. Other immune related factors, such as impaired immunometabolism, defective meningeal lymphatic vessels and autoimmunity might also be involved in the pathogenesis of AD. Here, we review the data showing the alterations of immune cells in the AD trajectory and seek to demonstrate the crosstalk between the immune cell dysfunction and AD pathology. We then discuss the most relevant research findings in regards to the influences of gene susceptibility of immune cells for AD. We also consider impaired meningeal lymphatics, immunometabolism and autoimmune mechanisms in AD. In addition, immune related biomarkers and immunotherapies for AD are also mentioned in order to offer novel insights for future research.