Structural basis for membrane attack complex inhibition by CD59

Enhanced retinal pigment epithelial cells as a delivery vehicle for retinal disease

Age-related macular degeneration (AMD) represents a major global health burden, with current estimates suggesting that up to 200 million people are affected globally. While effective treatments exist for the exudative form of the disease termed choroidal neovascular AMD, there remain challenges associated with long-term responses to treatment and the ongoing parallel development of the non-exudative form of AMD. Here, we sought to develop an approach for long-term delivery of both aflibercept, a decoy receptor that neutralises vascular endothelial growth factor and a concomitant treatment focused on treating the non-exudative form of AMD. To this end, we developed a series of induced pluripotent stem cell (iPS)-derived retinal pigment epithelial (RPE) cell lines that stably expressed aflibercept and/or sCD59. These cell lines were shown to produce high concentrations of both proteins. Sub-retinal injection of enhanced RPE cells potently prevented leakage of neovascular lesions in the JR5558 mouse model of retinal and choroidal neovascularization. Early results described here suggest that enhanced iPS-derived RPE cells could represent a novel approach to the long-term delivery of therapeutic agents to the eye.

Ficolin-1 in pediatric Plasmodium falciparum malaria and its possible role in parasite clearance and anemia

Plasmodium falciparum malaria causes significant disease, especially in young children. A successful immune response to P. falciparum is a major determinant of clinical outcome. The ficolins are a family of lectins that act as pattern recognition molecules and can activate the lectin complement pathway and may promote inflammation and facilitate opsonization and lysis of pathogens. Here, we have investigated the potential roles of ficolin-1 and ficolin-2 in the context of P. falciparum infection. We measured ficolin-1 and ficolin-2 concentrations in plasma from Malawian children presenting with uncomplicated or severe malaria or healthy controls (HCs) by ELISA. Using flow cytometry, we assessed whether ficolin-1 could bind to infected red blood cells (iRBCs) and whether it binds sialic acid on the iRBCs. Ficolin-1 and ficolin-2 plasma levels were measured in children from all clinical groups. Compared to HCs (reference), Ficolin-1 concentrations in plasma were higher in children with uncomplicated (geometric mean ratio: 1.88; 95% confidence interval [CI]: 1.25-2.82) and severe malaria (1.65; 95% CI: 1.10-2.46). Ficolin-1 levels were positively associated with peripheral blood monocyte (1.30; 1.02-1.67) and neutrophil counts (1.06; 1.00-1.13). Ficolin-2 was not associated with malaria. Hemoglobin levels were negatively associated with ficolin-1 (-0.38; -0.68 to -0.09) and ficolin-2 (-0.36; -0.68 to -0.04). Ficolin-1 bound more to iRBCs compared to uninfected RBCs, and binding was reduced in a ficolin-1 mutant that did not bind to sialic acid. These results highlight a largely overlooked role for ficolin-1 in the immune response to P. falciparum infection and point to a potential role for lectins contributing to parasite clearance and anaemia.

Glycosylation as an intricate post-translational modification process takes part in glycoproteins related immunity

Protein glycosylation, the most ubiquitous and diverse type of post-translational modification in eukaryotic cells, proteins are input into endoplasmic reticulum and Golgi apparatus for sorting and modification with intricate quality control, are then output for diverse functional glycoproteins that are utilized by cells to precisely regulate various biological processes. In order to maintain the precise spatial structure of glycoprotein, misfolded and unfolded glycoproteins are recognized, segregated and degraded to ensure the fidelity of protein folding and maturation. This review enumerates the role of five immune-related glycoproteins and reveals the relevance of glycosylation to their antigen presentation, immune effector function, immune recognition, receptor binding and activation, and cell adhesion and migration. With the knowledgement of glycoproteins in immune responses and etiologies, we propose several relevant therapeutic strategies on targeting glycosylation process for immunotherapy.

Stage-dependent proteomic alterations in aqueous humor of diabetic retinopathy patients based on data-independent acquisition and parallel reaction monitoring

BACKGROUND

Diabetic retinopathy (DR), a microvascular complication of diabetes mellitus (DM), represents the predominant cause of preventable vision loss in working-age populations globally. While the pathophysiological mechanisms underlying DR progression remain incompletely understood, our study employs comprehensive proteomic profiling of aqueous humor (AH) to identify stage-specific biomarkers and therapeutic targets in type 2 diabetes mellitus (T2DM) patients across DR progression.

METHODS

Utilizing data-independent acquisition (DIA) mass spectrometry, we quantified AH proteomes in a discovery cohort comprising 24 subjects: 18 T2DM patients stratified by DR severity [6 non-DR, 6 non-proliferative DR (NPDR), 6 proliferative DR (PDR)] and 6 cataract controls without diabetes (non-DM). Validation cohort analysis (including 10 AH samples in each group) was performed using parallel reaction monitoring (PRM) strategy for verification of target proteins. Comprehensive bioinformatics analyses included gene set enrichment analysis (GSEA), weighted gene co-expression network analysis (WGCNA), Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis, protein-protein interaction (PPI) network construction, receiver operating characteristic (ROC) curve analysis, and ConnectivityMap (Cmap)-based drug prediction.

RESULTS

Proteomic profiling identified 739 quantifiable AH proteins (62% extracellular) with clear separation among the four clinical stages in the discovery cohort. GSEA uncovered altered expression of proteins mainly related to complement and coagulation cascades, folate metabolism, and the selenium micronutrient network in patients with DR. WGCNA-derived protein modules yielded 83 PRM-validated targets, including 5 hub proteins differentiating NPDR from non-DR and 33 hub proteins showed significant upregulation in PDR versus NPDR comparison. Clinical correlation analysis identified F2, FGG, FGB, RBP4, AMBP, VTN, C8A, CPB2, and C2 associated with clinical traits. C6, FAM3C, SPP1, and JCHAIN levels were altered post-anti-VEGF treatment. Pharmacological prediction identified potential therapeutic compounds, including perindopril, triciribine, and XAV-939 for NPDR, and topiramate, triciribine, and vecuronium for PDR.

CONCLUSION

This study established a comprehensive AH proteomic signature of DR progression, offering insights into the pathogenesis of DR and highlighting potential biomarkers and novel therapeutic targets.

Macrocyclic Peptide Probes for Immunomodulatory Protein CD59: Potent Modulators of Bacterial Toxin Activity and Antibody-Dependent Cytotoxicity

CD59 is an immunomodulatory cell surface receptor associated with human disease. Despite its importance in complement regulation and bacterial pathogenesis, CD59 remains a challenging therapeutic target. Research to date has focused on antibody or protein-based strategies. Here we present a new approach to target CD59 using macrocyclic peptides with low nanomolar affinity for CD59. Through X-ray crystallographic studies and structure-activity relationship (SAR) studies, we identify key interactions that are essential for binding and activity. We find that the macrocyclic peptide CP-06 adopts a beta-hairpin structure and binds CD59 through an intermolecular beta-sheet, mimicking protein-protein interactions of biologically relevant CD59 interaction partners. We create dimeric and lipidated macrocyclic peptide conjugates as enhanced cell-active CD59 inhibitors and show that these probes can be used to modulate both complement-mediated killing of human cells and lytic activity of bacterial virulence factors. Together, our data provide a starting point for future development of macrocyclic peptides to target CD59 activity in diverse cellular contexts.

Expression of innate immunity genes in human hematopoietic stem/progenitor cells - single cell RNA-seq analysis

Background

The complement system expressed intracellularly and known as complosome has been indicated as a trigger in the regulation of lymphocyte functioning. The expression of its genes was confirmed also in several types of human bone marrow-derived stem cells: mononuclear cells (MNCs), very small embryonic-like stem cells (VSELs), hematopoietic stem/progenitor cells (HSPCs), endothelial progenitors (EPCs) and mesenchymal stem cells (MSCs). In our previous studies, we demonstrated the expression of complosome proteins including C3, C5, C3aR, and cathepsin L in purified HSPCs. However, there is still a lack of results showing the expression of complosome system elements and other immunity-related proteins in human HSPCs at the level of single cell resolution.

Methods

We employed scRNA-seq to investigate comprehensively the expression of genes connected with immunity, in two populations of human HSPCs: CD34+Lin-CD45+ and CD133+Lin-CD45+, with the division to subpopulations. We focused on genes coding complosome elements, selected cytokines, and genes related to antigen presentation as well as related to immune regulation.

Results

We observed the differences in the expression of several genes e.g. C3AR1 and C5AR1 between two populations of HSPCs: CD34+LinCD45+ and CD133+Lin-CD45+ resulting from their heterogeneous nature. However, in both kinds of HSPCs, we observed similar cell subpopulations expressing genes (e.g. NLRP3 and IL-1β) at the same level, which suggests the presence of cells performing similar functions connected with the activation of inflammatory processes contributing to the body's defense against infections.

Discussion

To our best knowledge, it is the first time that expression of complosome elements was studied in HSPCs at the single cell resolution with the use of single cell sequencing. Thus, our data sheds new light on complosome as a novel regulator of hematopoiesis that involves intracrine activation of the C5a-C5aR-Nlrp3 inflammasome axis.

Structural basis for the pore-forming activity of a complement-like toxin

Pore-forming proteins comprise a highly diverse group of proteins exemplified by the membrane attack complex/perforin (MACPF), cholesterol-dependent cytolysin (CDC), and gasdermin superfamilies, which all form gigantic pores (>150 angstroms). A recently found family of pore-forming toxins, called CDC-like proteins (CDCLs), are wide-spread in gut microbes and are a prevalent means of antibacterial antagonism. However, the structural aspects of how CDCLs assemble a pore remain a mystery. Here, we report the crystal structure of a proteolytically activated CDCL and cryo-electron microscopy structures of a prepore-like intermediate and a transmembrane pore providing detailed snapshots across the entire pore-forming pathway. These studies reveal a sophisticated array of regulatory features to ensure productive pore formation, and, thus, CDCLs straddle the MACPF, CDC, and gasdermin lineages of the giant pore superfamilies.

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.

Complement regulators as novel targets for anti-cancer therapy: A comprehensive review

Cancer remains a formidable global health challenge requiring the continued exploration of innovative therapeutic approaches. While traditional treatment strategies including surgery, chemotherapy, and radiation therapy have had some success, primarily in early-stage disease, the quest for more targeted, personalized, safer, and effective therapies remains an ongoing pursuit. Over the past decade, significant advances in the field of tumor immunology have dramatically shifted a focus towards immunotherapy, although the ability to harness and coopt the immune system to treat cancer is still just beginning to be realized. One important area that has yet to be fully explored is the complement system, an integral part of innate immunity that has gathered attention recently as a source of potential targets for anti-cancer therapy. The complement system has a complex and context dependent role in cancer biology in that it not only contributes to immune surveillance but also may promote tumor progression. Complement regulators, including CD46, CD55, CD59, and complement factor H, exercise defined control over complement activation, and have also been acknowledged for their role in the tumor microenvironment. This review explores the intricate role of complement regulators in cancer development and progression, examining their potential as therapeutic targets, current strategies, challenges, and the evolving landscape of clinical research.

Methods for detecting, building, and improving tryptophan mannosylation in glycoprotein structures

Tryptophan mannosylation, the covalent addition of an α-ᴅ-mannose sugar to a tryptophan side chain, is a post-translational modification (PTM) that can affect protein stability, folding, and interactions. Compared to other forms of protein glycosylation, it is relatively uncommon but is affected by conformational anomalies and modeling errors similar to those seen in N- and O-glycans in the Protein Data Bank (PDB). In this work, we report methods for detecting, building, and improving mannose structures linked to tryptophans. These methods have been used to mine X-ray crystallographic and cryo-electron microscopy maps in the PDB looking for unmodeled mannosylation, resulting in a number of cases where the modification can be placed in the map with high confidence. Additionally, we address most conformational issues affecting this modification. Finally, the development of a structural template to recognize thrombospondin repeats (TSR) domains where tryptophan mannosylation occurs will allow for the mannosylation of candidate-predicted models, for example, those predicted with AlphaFold.

Terminal complement complex deposition on chondrocytes promotes premature senescence in age- and trauma-related osteoarthritis

Background

The complement system is locally activated after joint injuries and leads to the deposition of the terminal complement complex (TCC). Sublytic TCC deposition is associated with phenotypical alterations of human articular chondrocytes (hAC) and enhanced release of inflammatory cytokines. Chronic inflammation is a known driver of chondrosenescence in osteoarthritis (OA). Therefore, we investigated whether TCC deposition contributes to stress-induced premature senescence (SIPS) during aging in vivo and after ex vivo cartilage injury.

Methods

Femoral condyles of male 13-week-old and 72-week-old CD59-ko (higher TCC deposition), C6-deficient (insufficient TCC formation), and C57BL/6 (WT) mice were collected to assess age-related OA. Furthermore, macroscopically intact human and porcine cartilage explants were traumatized and cultured with/without 30% human serum (HS) to activate the complement system. Explants were additionally treated with clusterin (CLU, TCC inhibitor), N-acetylcysteine (NAC, antioxidant), Sarilumab (IL-6 receptor inhibitor), STAT3-IN-1 (STAT3 inhibitor), or IL-1 receptor antagonist (IL-1RA) in order to investigate the consequences of TCC deposition. Gene and protein expression of senescence-associated markers such as CDKN1A and CDKN2A was determined.

Results

In the murine aging model, CD59-ko mice developed after 72 weeks more severe OA compared to C6-deficient and WT mice. mRNA analysis revealed that the expression of Cdkn1a, Cdkn2a, Tp53, Il1b, and Il6 was significantly increased in the cartilage of CD59-ko mice. In human cartilage, trauma and subsequent stimulation with HS increased mRNA levels of CDKN1A, CDKN2A, and IL6, while inhibition of TCC formation by CLU reduced the expression. Antioxidative therapy with NAC had no anti-senescent effect. In porcine tissue, HS exposure and trauma had additive effects on the number of CDKN2A-positive cells, while Sarilumab, STAT-IN-1, and IL-1RA reduced CDKN2A expression by trend.

Conclusion

Our results demonstrate that complement activation and consequent TCC deposition is associated with chondrosenescence in age-related and trauma-induced OA. We provided evidence that the SIPS-like phenotype is more likely induced by TCC-mediated cytokine release rather than oxidative stress. Overall, targeting TCC formation could be a future approach to attenuate OA progression.

Phase 1 Study of JNJ-81201887 Gene Therapy in Geographic Atrophy Secondary to Age-Related Macular Degeneration

PURPOSE

To evaluate the safety and tolerability of a single intravitreal injection of JNJ-81201887 (JNJ-1887) in patients with geographic atrophy (GA) secondary to advanced dry age-related macular degeneration (AMD).

DESIGN

Phase 1, open-label, single-center, first-in-human clinical study.

PARTICIPANTS

Adult patients (≥50 years of age) with GA secondary to AMD in the study-treated eye (treated eye) with Snellen best-corrected visual acuity of 20/200 or worse in the treated eye (20/80 or worse after the first 3 patients), a total GA lesion size between 5 and 20 mm2 (2-8 disc area), and best-corrected visual acuity of 20/800 or better in fellow, nontreated eye were included.

METHODS

Patients (n = 17) were enrolled sequentially into low-dose (3.56 × 1010 viral genome/eye; n = 3), intermediate-dose (1.07 × 1011 viral genome/eye; n = 3), and high-dose (3.56 × 1011 viral genome/eye; n = 11) cohorts without steroid prophylaxis and assessed for safety and tolerability over 24 months.

MAIN OUTCOME MEASURES

Safety and tolerability outcomes included assessment of ocular and nonocular treatment-emergent adverse events (AEs) over 24 months. Secondary outcomes included GA lesion size and growth rate.

RESULTS

Baseline patient characteristics were consistent with the disease under study, and all enrolled patients demonstrated foveal center-involved GA. JNJ-81201887 was well-tolerated across all cohorts, with no dose-limiting AEs. No serious or systemic AEs related to study intervention occurred. Overall, 5 of 17 patients (29%) experienced 5 events of mild ocular inflammation related to study treatment; examination findings in all resolved, and AEs resolved in 4 of 5 patients after topical steroids or observation. One unresolved vitritis event, managed with observation, occurred in a patient with an unrelated fatal AE. No endophthalmitis or new-onset choroidal neovascularization was reported. Geographic atrophy lesion growth rate was similar among all cohorts over 24 months. For treated eyes in the high-dose cohort, GA lesion growth rate showed continued decline through 24 months, with a reduction in mean square root lesion growth from 0.211 mm at months 0 through 6 to 0.056 mm at months 18 through 24.

CONCLUSIONS

All 3 studied doses of JNJ-1887 showed a manageable safety profile through 24 months of follow-up. Further investigation of JNJ-1887 for the treatment of GA is warranted.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Complement proteins and complement regulatory proteins are associated with age-related macular degeneration stage and treatment response

BACKGROUND

Dysregulation of the complement system is involved in development of age-related macular degeneration (AMD). The complement cascade is regulated by membrane bound complement regulatory proteins (Cregs) on mononuclear leukocytes among others. This study aims to investigate systemic complement proteins and Cregs in AMD stages and their association with treatment response in neovascular AMD (nAMD).

METHODS

In this clinical prospective study, treatment-naïve patients with nAMD, intermediate AMD (iAMD) and healthy controls were recruited and systemic complement proteins C3, C3a and C5a were investigated with electrochemiluminescence immunoassays, and Creg expression (CD35, CD46 and CD59) on T cells (CD4 + and CD8+) and monocytes (classical, intermediate and non-classical) investigated with flow cytometry. Treatment response in nAMD patients was evaluated after loading dose and after one year, and categorized as good, partial or poor. Complement proteins and Creg expression levels were compared between healthy controls, iAMD and nAMD, as well as between good, partial and poor nAMD treatment response groups. Polymorphisms in the CFH and ARMS2 genes were analyzed and compared to complement proteins and Creg expression levels in nAMD patients.

RESULTS

One hundred patients with nAMD, 34 patients with iAMD and 61 healthy controls were included. 94 nAMD patients completed the 1-year follow-up. Distribution of treatment response in nAMD was 61 (65%) good, 26 (28%) partial, and 7 (7%) poor responders. The distribution of 1-year treatment response was 50 (53%) good, 33 (36%) partial, and 11 (11%) poor responders. The concentrations of systemic C3, C3a, and the C3a/C3-ratio were significantly increased in patients with nAMD compared to healthy controls (P < 0.001, P = 0.002, and P = 0.035, respectively). Systemic C3 was also increased in iAMD compared to healthy controls (P = 0.031). The proportion of CD46 + CD4 + T cells and CD59 + intermediate monocytes were significantly decreased in patients with nAMD compared to healthy controls (P = 0.018 and P = 0.042, respectively). The post-loading dose partial treatment response group had significantly lower concentrations of C3a and C5a compared to the good response group (P = 0.005 and P = 0.042, respectively). The proportion of CD35 + monocytes was significantly lower in the 1-year partial response group compared to the 1-year good response group (P = 0.039). High-risk CFH genotypes in nAMD patients was associated with increased C3a, C3a/C3-ratio, and expression levels of CD35 + CD8 + T cells and CD46 + classical monocytes, while expression level of CD46 + non-classical monocytes was decreased.

CONCLUSION

Elevated concentrations of systemic complement proteins were found in patients with iAMD and nAMD. Decreased Creg expression levels were found in patients with nAMD. Partially responding nAMD patients had a dysregulated complement system and Cregs compared to good responders.

Plasma Glycated CD59 and Gestational Diabetes Mellitus: A Systematic Review

AIMS

Gestational diabetes mellitus (GDM) is a common complication of pregnancy worldwide. The standard method for screening GDM is the 75 g oral glucose tolerance test (OGTT). However, the OGTT is difficult, time-consuming and requires fasting, making it an inconvenient test for GDM. Researchers have turned their attention to alternative biomarkers for GDM. This study aimed to systematically investigate the potential of plasma glycated CD59 (pGCD59) as a new biomarker for GDM and its associated adverse pregnancy outcomes.

METHODS

The systematic review was performed in the PubMed, ISI Web of Science, Scopus and Google Scholar databases from 1/1/2000 to 4/1/2024, and relevant studies were selected based on the inclusion and exclusion criteria. The quality of the studies was assessed using the Newcastle-Ottawa scale.

RESULTS

The study revealed that pGCD59 levels before 20 weeks and during the second trimester of pregnancy have the potential to predict the results of the OGTT and also forecast adverse pregnancy outcomes, such as postpartum glucose intolerance (PP GI), neonatal hypoglycaemia (NH) and having large for gestational age (LGA) infants. The predictive ability of pGCD59 was found to be affected by the GDM status, especially body mass index (BMI).

CONCLUSIONS

In conclusion, pGCD59 may be a promising indicator of glucose levels and could serve as a new biomarker for GDM. However, additional studies are needed to establish a reliable reference range and cut-off value for pGCD59.

The complement system as a target in cancer immunotherapy

Malignant cells are part of a complex network within the tumor microenvironment, where their interaction with host cells and soluble mediators, including complement components, is pivotal. The complement system, known for its role in immune defense and homeostasis, exhibits a dual effect on cancer progression. This dichotomy arises from its antitumoral opsonophagocytosis and cytotoxicity versus its protumoral chronic inflammation mediated by the C5a/C5aR1 axis, influencing antitumor T-cell responses. Recent studies have revealed distinct co-expression patterns of complement genes in various cancer types, correlating with prognosis. Notably, some cancers exhibit co-regulated overexpression of complement genes associated with poor prognosis, while others show favorable outcomes. However, significant intra-patient heterogeneity further complicates this classification. Moreover, the involvement of locally produced and intracellular complement proteins adds complexity to the tumor microenvironment dynamics. This review highlights the unique interplay of complement components within different cancers and patient cohorts, showing that "one size does not fit all", for complement in cancer. It summarizes the clinical trials for complement targeting in cancer, emphasizing the need for tailored therapeutic approaches. By elucidating the mechanistic basis of complement's context-dependent role, this review aims to facilitate the development of personalized cancer therapies, ultimately improving patient care and outcomes.

Different Complement Activation Patterns Following C5 Cleavage in MOGAD and AQP4-IgG+NMOSD

OBJECTIVES

In myelin oligodendrocyte glycoprotein IgG-associated disease (MOGAD) and aquaporin-4 IgG+ neuromyelitis optica spectrum disorder (AQP4+NMOSD), the autoantibodies are mainly composed of IgG1, and complement-dependent cytotoxicity is a primary pathomechanism in AQP4+NMOSD. We aimed to evaluate the CSF complement activation in MOGAD.

METHODS

CSF-C3a, CSF-C4a, CSF-C5a, and CSF-C5b-9 levels during the acute phase before treatment in patients with MOGAD (n = 12), AQP4+NMOSD (n = 11), multiple sclerosis (MS) (n = 5), and noninflammatory neurologic disease (n = 2) were measured.

RESULTS

CSF-C3a and CSF-C5a levels were significantly higher in MOGAD (mean ± SD, 5,629 ± 1,079 pg/mL and 2,930 ± 435.8 pg/mL) and AQP4+NMOSD (6,017 ± 3,937 pg/mL and 2,544 ± 1,231 pg/mL) than in MS (1,507 ± 1,286 pg/mL and 193.8 ± 0.53 pg/mL). CSF-C3a, CSF-C4a, and CSF-C5a did not differ between MOGAD and AQP4+NMOSD while CSF-C5b-9 (membrane attack complex, MAC) levels were significantly lower in MOGAD (17.4 ± 27.9 ng/mL) than in AQP4+NMOSD (62.5 ± 45.1 ng/mL, p = 0.0019). Patients with MOGAD with severer attacks (Expanded Disability Status Scale [EDSS] ≥ 3.5) had higher C5b-9 levels (34.0 ± 38.4 ng/m) than those with milder attacks (EDSS ≤3.0, 0.9 ± 0.7 ng/mL, p = 0.044).

DISCUSSION

The complement pathway is activated in both MOGAD and AQP4+NMOSD, but MAC formation is lower in MOGAD, particularly in those with mild attacks, than in AQP4+NMOSD. These findings may have pathogenetic and therapeutic implications in MOGAD.

Downregulation of miRNA-26a by HIV-1 Enhances CD59 Expression and Packaging, Impacting Virus Susceptibility to Antibody-Dependent Complement-Mediated Lysis

MicroRNAs (miRNAs) play important roles in the control of HIV-1 infection. Here, we performed RNA-seq profiling of miRNAs and mRNAs expressed in CD4+ T lymphocytes upon HIV-1 infection. Our results reveal significant alterations in miRNA and mRNA expression profiles in infected relative to uninfected cells. One of the miRNAs markedly downregulated in infected cells is miRNA-26a. Among the putative targets of miRNA-26a are CD59 receptor transcripts, which are significantly upregulated in infected CD4+ T cells. The addition of miRNA-26a mimics to CD4+ T cells reduces CD59 at both the mRNA and surface protein levels, validating CD59 as a miRNA-26a target. Consistent with the reported inhibitory role of CD59 in complement-mediated lysis (CML), knocking out CD59 in CD4+ T cells renders both HIV-1-infected cells and progeny virions more prone to antibody-dependent CML (ADCML). The addition of miRNA-26a mimics to infected cells leads to enhanced sensitivity of progeny virions to ADCML, a condition linked to a reduction in CD59 packaging into released virions. Lastly, HIV-1-mediated downregulation of miRNA-26a expression is shown to be dependent on integrated HIV-1 expression but does not involve viral accessory proteins. Overall, these results highlight a novel mechanism by which HIV-1 limits ADCML by upregulating CD59 expression via miRNA-26a downmodulation.

CD59 Protects Primary Human Cerebrovascular Smooth Muscle Cells from Cytolytic Membrane Attack Complex

Cerebral amyloid angiopathy is characterized by a weakening of the small- and medium-sized cerebral arteries, as their smooth muscle cells are progressively replaced with acellular amyloid β, increasing vessel fragility and vulnerability to microhemorrhage. In this context, an aberrant overactivation of the complement system would further aggravate this process. The surface protein CD59 protects most cells from complement-induced cytotoxicity, but expression levels can fluctuate due to disease and varying cell types. The degree to which CD59 protects human cerebral vascular smooth muscle (HCSM) cells from complement-induced cytotoxicity has not yet been determined. To address this shortcoming, we selectively blocked the activity of HCSM-expressed CD59 with an antibody, and challenged the cells with complement, then measured cellular viability. Unblocked HCSM cells proved resistant to all tested concentrations of complement, and this resistance decreased progressively with increasing concentrations of anti-CD59 antibody. Complete CD59 blockage, however, did not result in a total loss of cellular viability, suggesting that additional factors may have some protective functions. Taken together, this implies that CD59 plays a predominant role in HCSM cellular protection against complement-induced cytotoxicity. The overexpression of CD59 could be an effective means of protecting these cells from excessive complement system activity, with consequent reductions in the incidence of microhemorrhage. The precise extent to which cellular repair mechanisms and other complement repair proteins contribute to this resistance has yet to be fully elucidated.

Distant relatives of a eukaryotic cell-specific toxin family evolved a complement-like mechanism to kill bacteria

Cholesterol-dependent cytolysins (CDCs) comprise a large family of pore-forming toxins produced by Gram-positive bacteria, which are used to attack eukaryotic cells. Here, we functionally characterize a family of 2-component CDC-like (CDCL) toxins produced by the Gram-negative Bacteroidota that form pores by a mechanism only described for the mammalian complement membrane attack complex (MAC). We further show that the Bacteroides CDCLs are not eukaryotic cell toxins like the CDCs, but instead bind to and are proteolytically activated on the surface of closely related species, resulting in pore formation and cell death. The CDCL-producing Bacteroides is protected from the effects of its own CDCL by the presence of a surface lipoprotein that blocks CDCL pore formation. These studies suggest a prevalent mode of bacterial antagonism by a family of two-component CDCLs that function like mammalian MAC and that are wide-spread in the gut microbiota of diverse human populations.

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.

Molecular mechanism of complement inhibition by the trypanosome receptor ISG65

African trypanosomes replicate within infected mammals where they are exposed to the complement system. This system centres around complement C3, which is present in a soluble form in serum but becomes covalently deposited onto the surfaces of pathogens after proteolytic cleavage to C3b. Membrane-associated C3b triggers different complement-mediated effectors which promote pathogen clearance. To counter complement-mediated clearance, African trypanosomes have a cell surface receptor, ISG65, which binds to C3b and which decreases the rate of trypanosome clearance in an infection model. However, the mechanism by which ISG65 reduces C3b function has not been determined. We reveal through cryogenic electron microscopy that ISG65 has two distinct binding sites for C3b, only one of which is available in C3 and C3d. We show that ISG65 does not block the formation of C3b or the function of the C3 convertase which catalyses the surface deposition of C3b. However, we show that ISG65 forms a specific conjugate with C3b, perhaps acting as a decoy. ISG65 also occludes the binding sites for complement receptors 2 and 3, which may disrupt recruitment of immune cells, including B cells, phagocytes, and granulocytes. This suggests that ISG65 protects trypanosomes by combining multiple approaches to dampen the complement cascade.

A guide to complement biology, pathology and therapeutic opportunity

Complement has long been considered a key innate immune effector system that mediates host defence and tissue homeostasis. Yet, growing evidence has illuminated a broader involvement of complement in fundamental biological processes extending far beyond its traditional realm in innate immunity. Complement engages in intricate crosstalk with multiple pattern-recognition and signalling pathways both in the extracellular and intracellular space. Besides modulating host-pathogen interactions, this crosstalk guides early developmental processes and distinct cell trajectories, shaping tissue immunometabolic and regenerative programmes in different physiological systems. This Review provides a guide to the system-wide functions of complement. It highlights illustrative paradigm shifts that have reshaped our understanding of complement pathobiology, drawing examples from evolution, development of the central nervous system, tissue regeneration and cancer immunity. Despite its tight spatiotemporal regulation, complement activation can be derailed, fuelling inflammatory tissue pathology. The pervasive contribution of complement to disease pathophysiology has inspired a resurgence of complement therapeutics with major clinical developments, some of which have challenged long-held dogmas. We thus highlight major therapeutic concepts and milestones in clinical complement intervention.

The complement cascade in lung injury and disease

BACKGROUND

The complement system is an important arm of immune defense bringing innate and adaptive immunity. Although originally regarded as a major complementary defense mechanism against pathogens, continuously emerging evidence has uncovered a central role of this complex system in several diseases including lung pathologies.

MAIN BODY

Complement factors such as anaphylatoxins C3a and C5a, their receptors C3aR, C5aR and C5aR2 as well as complement inhibitory proteins CD55, CD46 and CD59 have been implicated in pathologies such as the acute respiratory distress syndrome, pneumonia, chronic obstructive pulmonary disease, asthma, interstitial lung diseases, and lung cancer. However, the exact mechanisms by which complement factors induce these diseases remain unclear. Several complement-targeting monoclonal antibodies are reported to treat lung diseases.

CONCLUSIONS

The complement system contributes to the progression of the acute and chronic lung diseases. Better understanding of the underlying mechanisms will provide groundwork to develop new strategy to target complement factors for treatment of lung diseases.

Dynamics and Molecular Interactions of GPI-Anchored CD59

CD59 is a GPI-anchored cell surface receptor that serves as a gatekeeper to controlling pore formation. It is the only membrane-bound inhibitor of the complement membrane attack complex (MAC), an immune pore that can damage human cells. While CD59 blocks MAC pores, the receptor is co-opted by bacterial pore-forming proteins to target human cells. Recent structures of CD59 in complexes with binding partners showed dramatic differences in the orientation of its ectodomain relative to the membrane. Here, we show how GPI-anchored CD59 can satisfy this diversity in binding modes. We present a PyLipID analysis of coarse-grain molecular dynamics simulations of a CD59-inhibited MAC to reveal residues of complement proteins (C6:Y285, C6:R407 C6:K412, C7:F224, C8β:F202, C8β:K326) that likely interact with lipids. Using modules of the MDAnalysis package to investigate atomistic simulations of GPI-anchored CD59, we discover properties of CD59 that encode the flexibility necessary to bind both complement proteins and bacterial virulence factors.

Unveiling CD59-Antibody Interactions to Design Paratope-Mimicking Peptides for Complement Modulation

CD59 is an abundant immuno-regulatory human protein that protects cells from damage by inhibiting the complement system. CD59 inhibits the assembly of the Membrane Attack Complex (MAC), the bactericidal pore-forming toxin of the innate immune system. In addition, several pathogenic viruses, including HIV-1, escape complement-mediated virolysis by incorporating this complement inhibitor in their own viral envelope. This makes human pathogenic viruses, such as HIV-1, not neutralised by the complement in human fluids. CD59 is also overexpressed in several cancer cells to resist the complement attack. Consistent with its importance as a therapeutical target, CD59-targeting antibodies have been proven to be successful in hindering HIV-1 growth and counteracting the effect of complement inhibition by specific cancer cells. In this work, we make use of bioinformatics and computational tools to identify CD59 interactions with blocking antibodies and to describe molecular details of the paratope-epitope interface. Based on this information, we design and produce paratope-mimicking bicyclic peptides able to target CD59. Our results set the basis for the development of antibody-mimicking small molecules targeting CD59 with potential therapeutic interest as complement activators.