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Matola AT, Fülöp A, Rojkovich B, Nagy G, Sármay G, Józsi M, Uzonyi B. Autoantibodies against complement factor B in rheumatoid arthritis. Front Immunol 2023; 14:1113015. [PMID: 36891314 PMCID: PMC9986603 DOI: 10.3389/fimmu.2023.1113015] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Accepted: 01/23/2023] [Indexed: 02/22/2023] Open
Abstract
Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disorder affecting the joints. Many patients carry anti-citrullinated protein autoantibodies (ACPA). Overactivation of the complement system seems to be part of the pathogenesis of RA, and autoantibodies against the pathway initiators C1q and MBL, and the regulator of the complement alternative pathway, factor H (FH), were previously reported. Our aim was to analyze the presence and role of autoantibodies against complement proteins in a Hungarian RA cohort. To this end, serum samples of 97 ACPA-positive RA patients and 117 healthy controls were analyzed for autoantibodies against FH, factor B (FB), C3b, C3-convertase (C3bBbP), C1q, MBL and factor I. In this cohort, we did not detect any patient with FH autoantibodies but detected C1q autoantibodies in four patients, MBL autoantibodies in two patients and FB autoantibodies in five patients. Since the latter autoantibodies were previously reported in patients with kidney diseases but not in RA, we set out to further characterize such FB autoantibodies. The isotypes of the analyzed autoantibodies were IgG2, IgG3, IgGκ, IgGλ and their binding site was localized in the Bb part of FB. We detected in vivo formed FB-autoanti-FB complexes by Western blot. The effect of the autoantibodies on the formation, activity and FH-mediated decay of the C3 convertase in solid phase convertase assays was determined. In order to investigate the effect of the autoantibodies on complement functions, hemolysis assays and fluid phase complement activation assays were performed. The autoantibodies partially inhibited the complement-mediated hemolysis of rabbit red blood cells, inhibited the activity of the solid phase C3-convertase and C3 and C5b-9 deposition on complement activating surfaces. In summary, in ACPA-positive RA patients we identified FB autoantibodies. The characterized FB autoantibodies did not enhance complement activation, rather, they had inhibitory effect on complement. These results support the involvement of the complement system in the pathomechanism of RA and raise the possibility that protective autoantibodies may be generated in some patients against the alternative pathway C3 convertase. However, further analyses are needed to assess the exact role of such autoantibodies.
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Affiliation(s)
- Alexandra T Matola
- Department of Immunology, ELTE Eötvös Loránd University, Budapest, Hungary.,MTA-ELTE Complement Research Group, Eötvös Loránd Research Network (ELKH) at the Department of Immunology, ELTE Eötvös Loránd University, Budapest, Hungary
| | - Angéla Fülöp
- Buda Hospital of the Hospitaller Order of Saint John of God, Budapest, Hungary
| | | | - György Nagy
- Department of Rheumatology and Clinical Immunology, Semmelweis University, Budapest, Hungary.,Department of Internal Medicine and Oncology, Semmelweis University, Budapest, Hungary.,Heart and Vascular Center, Faculty of Medicine, Semmelweis University, Budapest, Hungary.,Department of Genetics, Cell- and Immunobiology, Faculty of Medicine, Semmelweis University, Budapest, Hungary
| | - Gabriella Sármay
- Department of Immunology, ELTE Eötvös Loránd University, Budapest, Hungary
| | - Mihály Józsi
- Department of Immunology, ELTE Eötvös Loránd University, Budapest, Hungary.,MTA-ELTE Complement Research Group, Eötvös Loránd Research Network (ELKH) at the Department of Immunology, ELTE Eötvös Loránd University, Budapest, Hungary
| | - Barbara Uzonyi
- Department of Immunology, ELTE Eötvös Loránd University, Budapest, Hungary.,MTA-ELTE Complement Research Group, Eötvös Loránd Research Network (ELKH) at the Department of Immunology, ELTE Eötvös Loránd University, Budapest, Hungary
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Kuźniewska A, Thiel M, Kowalska D, Felberg-Miętka A, Szynkowski P, Ołdziej S, Arjona E, Jongerius I, Rodriguez de Córdoba S, Okrój M, Urban A. Substitutions at position 263 within the von Willebrand factor type A domain determine the functionality of complement C2 protein. Front Immunol 2022; 13:1061696. [PMID: 36591303 PMCID: PMC9797810 DOI: 10.3389/fimmu.2022.1061696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Accepted: 11/28/2022] [Indexed: 12/23/2022] Open
Abstract
The complement system is one of the first defense lines protecting from invading pathogens. However, it may turn offensive to the body's own cells and tissues when deregulated by the presence of rare genetic variants that impair physiological regulation and/or provoke abnormal activity of key enzymatic components. Factor B and complement C2 are examples of paralogs engaged in the alternative and classical/lectin complement pathway, respectively. Pathogenic mutations in the von Willebrand factor A domain (vWA) of FB have been known for years. Despite substantial homology between two proteins and the demonstration that certain substitutions in FB translated to C2 result in analogous phenotype, there was a limited number of reports on pathogenic C2 variants in patients. Recently, we studied a cohort of patients suffering from rare kidney diseases and confirmed the existence of two gain-of-function and three loss-of-function mutations within the C2 gene sequences coding for the vWA domain (amino acids 254-452) or nearly located unstructured region (243-253) of C2 protein. Herein, we report the functional consequences of amino acid substitution of glutamine at position 263. The p.Q263G variant resulted in the gain-of-function phenotype, similarly to a homologous mutation p.D279G in FB. Conversely, the p.Q263P variant found in a patient with C3 glomerulopathy resulted in the loss of C2 function. Our results confirm that the N-terminal part of the vWA domain is a hot spot crucial for the complement C2 function.
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Affiliation(s)
- Alicja Kuźniewska
- Department of Cell Biology and Immunology, Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Gdańsk, Poland
| | - Marcel Thiel
- Department of Cell Biology and Immunology, Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Gdańsk, Poland
| | - Daria Kowalska
- Department of Cell Biology and Immunology, Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Gdańsk, Poland
| | - Anna Felberg-Miętka
- Department of Cell Biology and Immunology, Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Gdańsk, Poland
| | - Patryk Szynkowski
- Department of Cell Biology and Immunology, Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Gdańsk, Poland
| | - Stanisław Ołdziej
- Department of Cell Biology and Immunology, Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Gdańsk, Poland
| | - Emilia Arjona
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas and Centro de Investigación Biomédica en Enfermedades Raras, Madrid, Spain
| | - Ilse Jongerius
- Department of Pediatric Immunology, Rheumatology, and Infectious Diseases, Emma Children’s Hospital, Amsterdam University Medical Centre, Amsterdam, Netherlands,Department of Immunopathology, Sanquin Research, Landsteiner Laboratory, Amsterdam University Medical Centers (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Santiago Rodriguez de Córdoba
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas and Centro de Investigación Biomédica en Enfermedades Raras, Madrid, Spain
| | - Marcin Okrój
- Department of Cell Biology and Immunology, Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Gdańsk, Poland,*Correspondence: Marcin Okrój,
| | - Aleksandra Urban
- Department of Cell Biology and Immunology, Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Gdańsk, Poland,Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
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Biggs RM, Makou E, Lauder S, Herbert AP, Barlow PN, Katti SK. An Evaluation of the Complement-Regulating Activities of Human Complement Factor H (FH) Variants Associated With Age-Related Macular Degeneration. Invest Ophthalmol Vis Sci 2022; 63:30. [DOI: 10.1167/iovs.63.12.30] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Affiliation(s)
- Robyn M. Biggs
- Gemini Therapeutics, Inc., Cambridge, Massachusetts, United States
| | - Elisavet Makou
- School of Chemistry, University of Edinburgh, Edinburgh, United Kingdom
| | - Scott Lauder
- Gemini Therapeutics, Inc., Cambridge, Massachusetts, United States
| | - Andrew P. Herbert
- School of Chemistry, University of Edinburgh, Edinburgh, United Kingdom
| | - Paul N. Barlow
- School of Chemistry, University of Edinburgh, Edinburgh, United Kingdom
- School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Suresh K. Katti
- Gemini Therapeutics, Inc., Cambridge, Massachusetts, United States
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Ries JI, Heß M, Nouri N, Wichelhaus TA, Göttig S, Falcone FH, Kraiczy P. CipA mediates complement resistance of Acinetobacter baumannii by formation of a factor I-dependent quadripartite assemblage. Front Immunol 2022; 13:942482. [PMID: 35958553 PMCID: PMC9361855 DOI: 10.3389/fimmu.2022.942482] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 06/24/2022] [Indexed: 11/29/2022] Open
Abstract
Multidrug-resistant Acinetobacter baumannii is known to be one of the leading pathogens that cause severe nosocomial infections. To overcome eradication by the innate immune system during infection, A. baumannii developed a number of immune evasion strategies. Previously, we identified CipA as a plasminogen-binding and complement-inhibitory protein. Here we show that CipA inhibits all three complement activation pathways and interacts with key complement components C3, C3b, C4b, C5, Factor B, Factor D, and in particular Factor I. CipA also targets function of the C5 convertase as cleavage of C5 was impaired. Systematic screening of CipA variants identified two separate binding sites for C3b and a Factor I-interacting domain located at the C-terminus. Structure predictions using AlphaFold2 and binding analyses employing CipA variants lacking Factor I-binding capability confirmed that the orientation of the C-terminal domain is essential for the interaction with Factor I. Hence, our analyses point to a novel Factor I-dependent mechanisms of complement inactivation mediated by CipA of A. baumannii. Recruitment of Factor I by CipA initiates the assembly of a quadripartite complex following binding of either Factor H or C4b-binding protein to degrade C3b and C4b, respectively. Loss of Factor I binding in a CipA-deficient strain, or a strain producing a CipA variant lacking Factor I-binding capability, correlated with a higher susceptibility to human serum, indicating that recruitment of Factor I enables A. baumannii to resist complement-mediated killing.
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Affiliation(s)
- Julia I. Ries
- Institute of Medical Microbiology and Infection Control, University Hospital of Frankfurt, Goethe University Frankfurt, Frankfurt, Germany
| | - Marie Heß
- Institute of Medical Microbiology and Infection Control, University Hospital of Frankfurt, Goethe University Frankfurt, Frankfurt, Germany
| | - Noura Nouri
- Institute of Medical Microbiology and Infection Control, University Hospital of Frankfurt, Goethe University Frankfurt, Frankfurt, Germany
| | - Thomas A. Wichelhaus
- Institute of Medical Microbiology and Infection Control, University Hospital of Frankfurt, Goethe University Frankfurt, Frankfurt, Germany
| | - Stephan Göttig
- Institute of Medical Microbiology and Infection Control, University Hospital of Frankfurt, Goethe University Frankfurt, Frankfurt, Germany
| | - Franco H. Falcone
- Institute for Parasitology, Biomedical Research Center Seltersberg, Justus Liebig University Giessen, Giessen, Germany
| | - Peter Kraiczy
- Institute of Medical Microbiology and Infection Control, University Hospital of Frankfurt, Goethe University Frankfurt, Frankfurt, Germany
- *Correspondence: Peter Kraiczy,
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Lee JD, Woodruff TM. The emerging role of complement in neuromuscular disorders. Semin Immunopathol 2021; 43:817-828. [PMID: 34705082 DOI: 10.1007/s00281-021-00895-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Accepted: 09/22/2021] [Indexed: 12/14/2022]
Abstract
The complement cascade is a key arm of the immune system that protects the host from exogenous and endogenous toxic stimuli through its ability to potently regulate inflammation, phagocytosis, and cell lysis. Due to recent clinical trial successes and drug approvals for complement inhibitors, there is a resurgence in targeting complement as a therapeutic approach to prevent ongoing tissue destruction in several diseases. In particular, neuromuscular diseases are undergoing a recent focus, with demonstrated links between complement activation and disease pathology. This review aims to provide a comprehensive overview of complement activation and its role during the initiation and progression of neuromuscular disorders including myasthenia gravis, amyotrophic lateral sclerosis, and Duchenne muscular dystrophy. We will review the preclinical and clinical evidence for complement in these diseases, with an emphasis on the complement-targeting drugs in clinical trials for these indications.
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Affiliation(s)
- John D Lee
- School of Biomedical Sciences, The University of Queensland, St Lucia, Brisbane, QLD, 4072, Australia.
| | - Trent M Woodruff
- School of Biomedical Sciences, The University of Queensland, St Lucia, Brisbane, QLD, 4072, Australia.,Queensland Brain Institute, The University of Queensland, St Lucia, Brisbane, QLD, 4072, Australia
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Kim BJ, Mastellos DC, Li Y, Dunaief JL, Lambris JD. Targeting complement components C3 and C5 for the retina: Key concepts and lingering questions. Prog Retin Eye Res 2021; 83:100936. [PMID: 33321207 PMCID: PMC8197769 DOI: 10.1016/j.preteyeres.2020.100936] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 12/07/2020] [Accepted: 12/09/2020] [Indexed: 12/13/2022]
Abstract
Age-related macular degeneration (AMD) remains a major cause of legal blindness, and treatment for the geographic atrophy form of AMD is a significant unmet need. Dysregulation of the complement cascade is thought to be instrumental for AMD pathophysiology. In particular, C3 and C5 are pivotal components of the complement cascade and have become leading therapeutic targets for AMD. In this article, we discuss C3 and C5 in detail, including their roles in AMD, biochemical and structural aspects, locations of expression, and the functions of C3 and C5 fragments. Further, the article critically reviews developing therapeutics aimed at C3 and C5, underscoring the potential effects of broad inhibition of complement at the level of C3 versus more specific inhibition at C5. The relationships of complement biology to the inflammasome and microglia/macrophage activity are highlighted. Concepts of C3 and C5 biology will be emphasized, while we point out questions that need to be settled and directions for future investigations.
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Affiliation(s)
- Benjamin J Kim
- Scheie Eye Institute, Department of Ophthalmology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
| | | | - Yafeng Li
- Scheie Eye Institute, Department of Ophthalmology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Joshua L Dunaief
- Scheie Eye Institute, Department of Ophthalmology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - John D Lambris
- Department of Laboratory Medicine and Pathology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
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Mantegazza R, Vanoli F, Frangiamore R, Cavalcante P. Complement Inhibition for the Treatment of Myasthenia Gravis. Immunotargets Ther 2020; 9:317-331. [PMID: 33365280 PMCID: PMC7751298 DOI: 10.2147/itt.s261414] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2020] [Accepted: 12/02/2020] [Indexed: 12/11/2022] Open
Abstract
Generalized myasthenia gravis (gMG) is a rare autoimmune disorder affecting the neuromuscular junction (NMJ). Approximately 80-90% of patients display antibodies directed against the nicotinic acetylcholine receptor (AChR). A major drive of AChR antibody-positive MG pathology is represented by complement activation. The role of the complement cascade has been largely demonstrated in patients and in MG animal models. Complement activation at the NMJ leads to focal lysis of the post-synaptic membrane, disruption of the characteristic folds, and reduction of AChR. Given that the complement system works as an activation cascade, there are many potential targets that can be considered for therapeutic intervention. Preclinical studies have confirmed the efficacy of complement inhibition in ameliorating MG symptoms. Eculizumab, an antibody directed towards C5, has recently been approved for the treatment of AChR antibody-positive gMG. Other complement inhibitors, targeting C5 as well, are currently under phase III study. Complement inhibitors, however, may present prohibitive costs. Therefore, the identification of a subset of patients more or less prone to respond to such therapies would be beneficial. For such purpose, there is a critical need to identify possible biomarkers predictive of therapeutic response, a field not yet sufficiently explored in MG. This review aims to give an overview of the complement cascade involvement in MG, the evolution of complement-inhibiting therapies and possible biomarkers useful to tailor and monitor complement-directed therapies.
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Affiliation(s)
- Renato Mantegazza
- Neurology IV - Neuroimmunology and Neuromuscular Diseases Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Fiammetta Vanoli
- Neurology IV - Neuroimmunology and Neuromuscular Diseases Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Rita Frangiamore
- Neurology IV - Neuroimmunology and Neuromuscular Diseases Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Paola Cavalcante
- Neurology IV - Neuroimmunology and Neuromuscular Diseases Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
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Yuan K, Ye J, Liu Z, Ren Y, He W, Xu J, He Y, Yuan Y. Complement C3 overexpression activates JAK2/STAT3 pathway and correlates with gastric cancer progression. JOURNAL OF EXPERIMENTAL & CLINICAL CANCER RESEARCH : CR 2020; 39:9. [PMID: 31928530 PMCID: PMC6956509 DOI: 10.1186/s13046-019-1514-3] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Accepted: 12/22/2019] [Indexed: 12/21/2022]
Abstract
Background Localized C3 deposition is a well-known factor of inflammation. However, its role in oncoprogression of gastric cancer (GC) remains obscured. This study aims to explore the prognostic value of C3 deposition and to elucidate the mechanism of C3-related oncoprogression for GC. Methods From August to December 2013, 106 GC patients were prospectively included. The regional expression of C3 and other effectors in gastric tissues were detected by WB, IHC, qRT-PCR and other tests. The correlation of localized C3 deposition and oncologic outcomes was determined by 5-year survival significance. Human GC and normal epithelial cell lines were employed to detect a relationship between C3 and STAT3 signaling pathway in vitro experiments. Results C3 and C3a expression were markedly enhanced in GC tissues at both mRNA and protein levels compared with those in paired nontumorous tissues. According to IHC C3 score, 65 (61.3%) and 41 (38.7%) patients had high and low C3 deposition, respectively. C3 deposition was negatively correlated with plasma levels of C3 and C3a (both P < 0.001) and positively correlated with pathological T and TNM stages (both P < 0.001). High C3 deposition was identified as an independent prognostic factor of poor 5-year overall survival (P = 0.045). In vitro C3 administration remarkably enhanced p-JAK2/p-STAT3 expression in GC cell lines but caused a reduction of such activation when pre-incubated with a C3 blocker. Importantly, C3 failed to activate such signaling in cells pre-treated with a JAK2 inhibitor. Conclusions Localized C3 deposition in the tumor microenvironment is a relevant immune signature for predicting prognosis of GC. It may aberrantly activate JAK2/STAT3 pathway allowing oncoprogression. Trial registration ClinicalTrials.gov, NCT02425930, Registered 1st August 2013.
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Affiliation(s)
- Kaitao Yuan
- Center of Gastrointestinal Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, People's Republic of China.,Center of Gastric cancer, Sun Yat-sen University, Guangzhou, People's Republic of China
| | - Jinning Ye
- Center of Gastrointestinal Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, People's Republic of China.,Center of Gastric cancer, Sun Yat-sen University, Guangzhou, People's Republic of China
| | - Zhenguo Liu
- Department of Thoracic Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, People's Republic of China
| | - Yufeng Ren
- Department of Radiation Oncology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, People's Republic of China
| | - Weiling He
- Center of Gastrointestinal Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, People's Republic of China. .,Center of Gastric cancer, Sun Yat-sen University, Guangzhou, People's Republic of China.
| | - Jianbo Xu
- Center of Gastrointestinal Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, People's Republic of China. .,Center of Gastric cancer, Sun Yat-sen University, Guangzhou, People's Republic of China.
| | - Yulong He
- Center of Gastrointestinal Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, People's Republic of China. .,Center of Gastric cancer, Sun Yat-sen University, Guangzhou, People's Republic of China.
| | - Yujie Yuan
- Center of Gastrointestinal Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, People's Republic of China. .,Center of Gastric cancer, Sun Yat-sen University, Guangzhou, People's Republic of China.
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Molecular engineering of an efficient four-domain DAF-MCP chimera reveals the presence of functional modularity in RCA proteins. Proc Natl Acad Sci U S A 2019; 116:9953-9958. [PMID: 31036650 DOI: 10.1073/pnas.1818573116] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The complement system is highly efficient in targeting pathogens, but lack of its apposite regulation results in host-cell damage, which is linked to diseases. Thus, complement activation is tightly regulated by a series of proteins, which primarily belong to the regulators of complement activation (RCA) family. Structurally, these proteins are composed of repeating complement control protein (CCP) domains where two to four successive domains contribute to the regulatory functions termed decay-accelerating activity (DAA) and cofactor activity (CFA). However, the precise constitution of the functional units and whether these units can be joined to form a larger composition with dual function have not been demonstrated. Herein, we have parsed the functional units for DAA and CFA by constructing chimeras of the decay-accelerating factor (DAF) that exhibits DAA and membrane cofactor protein (MCP) that exhibits CFA. We show that in a four-CCP framework, a functional unit for each of the regulatory activities is formed by only two successive CCPs wherein each participates in the function, albeit CCP2 has a bipartite function. Additionally, optimal activity requires C-terminal domains that enhance the avidity of the molecule for C3b/C4b. Furthermore, by composing a four-CCP DAF-MCP chimera with robust CFA (for C3b and C4b) and DAA (for classical and alternative pathway C3 convertases), named decay cofactor protein, we show that CCP functional units can be linked to design a dual-activity regulator. These data indicate that the regulatory determinants for these two biological processes are distinct and modular in nature.
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Donadelli R, Pulieri P, Piras R, Iatropoulos P, Valoti E, Benigni A, Remuzzi G, Noris M. Unraveling the Molecular Mechanisms Underlying Complement Dysregulation by Nephritic Factors in C3G and IC-MPGN. Front Immunol 2018; 9:2329. [PMID: 30487789 PMCID: PMC6248175 DOI: 10.3389/fimmu.2018.02329] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 09/19/2018] [Indexed: 01/08/2023] Open
Abstract
Membranoproliferative glomerulonephritis (MPGN) was recently classified as C3 glomerulopathies (C3G), and immune-complex (IC) mediated MPGN. Dysregulation of the complement alternative pathway, driven by acquired and/or genetic defects, plays a pathogenetic role in C3G. However, alternative pathway abnormalities were also found in IC-MPGN. The most common acquired drivers are the C3 nephritic factors (C3NeFs), heterogeneous autoantibodies that stabilize the C3 convertase, C3bBb. C3NeFs are traditionally detected by hemolytic assays based on sheep erythrocyte lysis, which however do not provide a direct molecular estimation of C3bBb formation and decay. We set up a microplate/western blot assay that specifically detects and quantifies C3bBb, and its precursor, the C3 proconvertase C3bB, to investigate the complex mechanistic effects of C3NeFs from patients with primary IC-MPGN (n = 13) and C3G (n = 13). In the absence of properdin, 9/26 patients had C3NeF IgGs stabilizing C3bBb against spontaneous and FH-accelerated decay. In the presence of properdin the IgGs of all but one patient had C3bBb-stabilizing activity. Properdin-independent C3NeFs were identified mostly in DDD patients, while properdin-dependent C3NeFs associated with either C3GN or IC-MPGN and with higher incidence of nephrotic syndrome. When we grouped patients based on our recent cluster analysis, patients in cluster 3, with highly electron-dense intramembranous deposits, low C3, and mostly normal sC5b-9 levels, had a higher prevalence of properdin-independent C3NeFs than patients in clusters 1 and 2. Conversely, about 70% of cluster 1 and 2 patients, with subendothelial, subepithelial, and mesangial deposits, low C3 levels and high sC5b-9 levels, had properdin-dependent C3NeFs. The flexibility of the assay allowed us to get deep insights into C3NeF mechanisms of action, showing that: (1) most C3NeFs bind strongly and irreversibly to C3 convertase; (2) C3NeFs and FH recognize different epitopes in C3 convertase; (3) C3NeFs bind rapidly to C3 convertase and antagonize the decay accelerating activity of FH on newly formed complexes; (4) C3NeFs do not affect formation and stability of the C3 proconvertase. Thus, our study provides a molecular approach to detecting and characterizing C3NeFs. The results highlight different mechanisms of complement dysregulation resulting in different complement profiles and patterns of glomerular injury, and this may have therapeutic implications.
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Affiliation(s)
- Roberta Donadelli
- Clinical Research Center for Rare Diseases Aldo e Cele Daccò and Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Patrizia Pulieri
- Clinical Research Center for Rare Diseases Aldo e Cele Daccò and Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Rossella Piras
- Clinical Research Center for Rare Diseases Aldo e Cele Daccò and Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Paraskevas Iatropoulos
- Clinical Research Center for Rare Diseases Aldo e Cele Daccò and Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Elisabetta Valoti
- Clinical Research Center for Rare Diseases Aldo e Cele Daccò and Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Ariela Benigni
- Clinical Research Center for Rare Diseases Aldo e Cele Daccò and Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Giuseppe Remuzzi
- Clinical Research Center for Rare Diseases Aldo e Cele Daccò and Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy.,Unit of Nephrology and Dialysis, Azienda Socio-Sanitaria Territoriale Papa Giovanni XXIII, Bergamo, Italy.,Department of Biomedical and Clinical Sciences, University of Milan, Milan, Italy
| | - Marina Noris
- Clinical Research Center for Rare Diseases Aldo e Cele Daccò and Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
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Kusner LL, Sengupta M, Kaminski HJ. Acetylcholine receptor antibody-mediated animal models of myasthenia gravis and the role of complement. Ann N Y Acad Sci 2018; 1413:136-142. [PMID: 29356015 DOI: 10.1111/nyas.13555] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 10/23/2017] [Accepted: 10/25/2017] [Indexed: 12/22/2022]
Abstract
Because of the failure of many promising therapeutics identified in preclinical evaluation, funding sources have established guidelines for increased rigor in animal evaluations. The myasthenia gravis (MG) community of scientists has developed guidelines for preclinical assessment for potential MG treatments. Here, we provide a focused summary of these recommendations and the role of complement in disease development in experimental models of MG.
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Affiliation(s)
- Linda L Kusner
- Department of Pharmacology and Physiology, George Washington University School of Medicine and Health Sciences, Washington, DC
| | - Manjistha Sengupta
- Department of Neurology, George Washington University School of Medicine and Health Sciences, Washington, DC
| | - Henry J Kaminski
- Department of Neurology, George Washington University School of Medicine and Health Sciences, Washington, DC
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12
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Cernoch M, Viklicky O. Complement in Kidney Transplantation. Front Med (Lausanne) 2017; 4:66. [PMID: 28611987 PMCID: PMC5447724 DOI: 10.3389/fmed.2017.00066] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Accepted: 05/09/2017] [Indexed: 12/12/2022] Open
Abstract
The complement system is considered to be an important part of innate immune system with a significant role in inflammation processes. The activation can occur through classical, alternative, or lectin pathway, resulting in the creation of anaphylatoxins C3a and C5a, possessing a vast spectrum of immune functions, and the assembly of terminal complement cascade, capable of direct cell lysis. The activation processes are tightly regulated; inappropriate activation of the complement cascade plays a significant role in many renal diseases including organ transplantation. Moreover, complement cascade is activated during ischemia/reperfusion injury processes and influences delayed graft function of kidney allografts. Interestingly, complement system has been found to play a role in both acute cellular and antibody-mediated rejections and thrombotic microangiopathy. Therefore, complement system may represent an interesting therapeutical target in kidney transplant pathologies.
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Affiliation(s)
- Marek Cernoch
- Transplant Laboratory, Transplant Center, Institute for Clinical and Experimental Medicine, Prague, Czechia
| | - Ondrej Viklicky
- Transplant Laboratory, Transplant Center, Institute for Clinical and Experimental Medicine, Prague, Czechia.,Department of Nephrology, Transplant Center, Institute for Clinical and Experimental Medicine, Prague, Czechia
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13
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Bettoni S, Bresin E, Remuzzi G, Noris M, Donadelli R. Insights into the Effects of Complement Factor H on the Assembly and Decay of the Alternative Pathway C3 Proconvertase and C3 Convertase. J Biol Chem 2016; 291:8214-30. [PMID: 26903516 DOI: 10.1074/jbc.m115.693119] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Indexed: 12/12/2022] Open
Abstract
The activated fragment of C3 (C3b) and factor B form the C3 proconvertase (C3bB), which is cleaved by factor D to C3 convertase (C3bBb). Older studies (Conrad, D. H., Carlo, J. R., and Ruddy, S. (1978)J. Exp. Med.147, 1792-1805; Pangburn, M. K., and Müller-Eberhard, H. J. (1978)Proc. Natl. Acad. Sci. U.S.A.75, 2416-2420; Kazatchkine, M. D., Fearon, D. T., and Austen, K. F. (1979)J. Immunol.122, 75-81) indicated that the complement alternative pathway regulator factor H (FH) competes with factor B for C3b binding; however, the capability of FH to prevent C3bB assembly has not been formally investigated. Moreover, in the few published studies FH did not favor C3bB dissociation. Whether FH may affect C3bBb formation from C3bB is unknown. We set up user-friendly assays based on combined microplate/Western blotting techniques that specifically detect either C3bB or C3bBb, with the aim of investigating the effect of FH on C3bB assembly and decay and C3bBb formation and decay. We document that FH does not affect C3bB assembly, indicating that FH does not efficiently compete with factor B for C3b binding. We also found that FH does not dissociate C3bB. FH showed a strong C3bBb decay-accelerating activity, as reported previously, and also exerted an apparent inhibitory effect on C3bBb formation. The latter effect was not fully attributable to a rapid FH-mediated dissociation of C3bBb complexes, because blocking decay with properdin and C3 nephritic factor did not restore C3bBb formation. FH almost completely prevented release of the smaller cleavage subunit of FB (Ba), without modifying the amount of C3bB complexes, suggesting that FH inhibits the conversion of C3bB to C3bBb. Thus, the inhibitory effect of FH on C3bBb formation is likely the sum of inhibition of C3bB conversion to C3bBb and of C3bBb decay acceleration. Further studies are required to confirm these findings in physiological cell-based settings.
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Affiliation(s)
- Serena Bettoni
- From the IRCCS-Istituto di Ricerche Farmacologiche Mario Negri, Clinical Research Center for Rare Diseases Aldo e Cele Daccò, 24020 Ranica, Bergamo
| | - Elena Bresin
- From the IRCCS-Istituto di Ricerche Farmacologiche Mario Negri, Clinical Research Center for Rare Diseases Aldo e Cele Daccò, 24020 Ranica, Bergamo
| | - Giuseppe Remuzzi
- From the IRCCS-Istituto di Ricerche Farmacologiche Mario Negri, Clinical Research Center for Rare Diseases Aldo e Cele Daccò, 24020 Ranica, Bergamo, the Azienda Ospedaliera Papa Giovanni XXIII, Unit of Nephrology and Dialysis, 24127 Bergamo, and the Department of Biomedical and Clinical Sciences, University of Milan, 20157 Milan, Italy
| | - Marina Noris
- From the IRCCS-Istituto di Ricerche Farmacologiche Mario Negri, Clinical Research Center for Rare Diseases Aldo e Cele Daccò, 24020 Ranica, Bergamo,
| | - Roberta Donadelli
- From the IRCCS-Istituto di Ricerche Farmacologiche Mario Negri, Clinical Research Center for Rare Diseases Aldo e Cele Daccò, 24020 Ranica, Bergamo
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14
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Java A, Liszewski MK, Hourcade DE, Zhang F, Atkinson JP. Role of complement receptor 1 (CR1; CD35) on epithelial cells: A model for understanding complement-mediated damage in the kidney. Mol Immunol 2015; 67:584-95. [PMID: 26260209 DOI: 10.1016/j.molimm.2015.07.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Revised: 07/07/2015] [Accepted: 07/16/2015] [Indexed: 12/27/2022]
Abstract
The regulators of complement activation gene cluster encodes a group of proteins that have evolved to control the amplification of complement at the critical step of C3 activation. Complement receptor 1 (CR1) is the most versatile of these inhibitors with both receptor and regulatory functions. While expressed on most peripheral blood cells, the only epithelial site of expression in the kidney is by the podocyte. Its expression by this cell population has aroused considerable speculation as to its biologic function in view of many complement-mediated renal diseases. The goal of this investigation was to assess the role of CR1 on epithelial cells. To this end, we utilized a Chinese hamster ovary cell model system. Among our findings, CR1 reduced C3b deposition by ∼ 80% during classical pathway activation; however, it was an even more potent regulator (>95% reduction in C3b deposition) of the alternative pathway. This inhibition was primarily mediated by decay accelerating activity. The deposited C4b and C3b were progressively cleaved with a t½ of ∼ 30 min to C4d and C3d, respectively, by CR1-dependent cofactor activity. CR1 functioned intrinsically (i.e, worked only on the cell on which it was expressed). Moreover, CR1 efficiently and stably bound but didn't internalize C4b/C3b opsonized immune complexes. Our studies underscore the potential importance of CR1 on an epithelial cell population as both an intrinsic complement regulator and an immune adherence receptor. These results provide a framework for understanding how loss of CR1 expression on podocytes may contribute to complement-mediated damage in the kidney.
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Affiliation(s)
- Anuja Java
- Washington University School of Medicine, Department of Internal Medicine, Division of Nephrology, 660 South Euclid Avenue, St. Louis, MO 63110 USA.
| | - M Kathryn Liszewski
- Department of Internal Medicine, Division of Rheumatology, 660 South Euclid Avenue, St. Louis, MO 63110 USA.
| | - Dennis E Hourcade
- Department of Internal Medicine, Division of Rheumatology, 660 South Euclid Avenue, St. Louis, MO 63110 USA.
| | - Fan Zhang
- Department of Internal Medicine, Division of Rheumatology, 660 South Euclid Avenue, St. Louis, MO 63110 USA.
| | - John P Atkinson
- Department of Internal Medicine, Division of Rheumatology, 660 South Euclid Avenue, St. Louis, MO 63110 USA.
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15
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Merle NS, Church SE, Fremeaux-Bacchi V, Roumenina LT. Complement System Part I - Molecular Mechanisms of Activation and Regulation. Front Immunol 2015; 6:262. [PMID: 26082779 PMCID: PMC4451739 DOI: 10.3389/fimmu.2015.00262] [Citation(s) in RCA: 960] [Impact Index Per Article: 106.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Accepted: 05/11/2015] [Indexed: 12/12/2022] Open
Abstract
Complement is a complex innate immune surveillance system, playing a key role in defense against pathogens and in host homeostasis. The complement system is initiated by conformational changes in recognition molecular complexes upon sensing danger signals. The subsequent cascade of enzymatic reactions is tightly regulated to assure that complement is activated only at specific locations requiring defense against pathogens, thus avoiding host tissue damage. Here, we discuss the recent advances describing the molecular and structural basis of activation and regulation of the complement pathways and their implication on physiology and pathology. This article will review the mechanisms of activation of alternative, classical, and lectin pathways, the formation of C3 and C5 convertases, the action of anaphylatoxins, and the membrane-attack-complex. We will also discuss the importance of structure-function relationships using the example of atypical hemolytic uremic syndrome. Lastly, we will discuss the development and benefits of therapies using complement inhibitors.
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Affiliation(s)
- Nicolas S Merle
- UMR_S 1138, Cordeliers Research Center, Complement and Diseases Team, INSERM , Paris , France ; UMR_S 1138, Centre de Recherche des Cordeliers, Sorbonne Paris Cité, Université Paris Descartes , Paris , France ; UMR_S 1138, Centre de Recherche des Cordeliers, Sorbonne Universités, Université Pierre et Marie Curie-Paris , Paris , France
| | - Sarah Elizabeth Church
- UMR_S 1138, Centre de Recherche des Cordeliers, Sorbonne Paris Cité, Université Paris Descartes , Paris , France ; UMR_S 1138, Centre de Recherche des Cordeliers, Sorbonne Universités, Université Pierre et Marie Curie-Paris , Paris , France ; UMR_S 1138, Cordeliers Research Center, Integrative Cancer Immunology Team, INSERM , Paris , France
| | - Veronique Fremeaux-Bacchi
- UMR_S 1138, Cordeliers Research Center, Complement and Diseases Team, INSERM , Paris , France ; UMR_S 1138, Centre de Recherche des Cordeliers, Sorbonne Paris Cité, Université Paris Descartes , Paris , France ; UMR_S 1138, Centre de Recherche des Cordeliers, Sorbonne Universités, Université Pierre et Marie Curie-Paris , Paris , France ; Service d'Immunologie Biologique, Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges-Pompidou , Paris , France
| | - Lubka T Roumenina
- UMR_S 1138, Cordeliers Research Center, Complement and Diseases Team, INSERM , Paris , France ; UMR_S 1138, Centre de Recherche des Cordeliers, Sorbonne Paris Cité, Université Paris Descartes , Paris , France ; UMR_S 1138, Centre de Recherche des Cordeliers, Sorbonne Universités, Université Pierre et Marie Curie-Paris , Paris , France
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16
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Sheta EA, Appel SH, Goldknopf IL. 2D gel blood serum biomarkers reveal differential clinical proteomics of the neurodegenerative diseases. Expert Rev Proteomics 2014; 3:45-62. [PMID: 16445350 DOI: 10.1586/14789450.3.1.45] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This review addresses the challenges of neuroproteomics and recent progress in biomarkers and tests for neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. The review will discuss how the application of quantitative 2D gel electrophoresis, combined with appropriate single-variable and multivariate biostatistics, allows for selection of disease-specific serum biomarkers. It will also address how the use of large cohorts of specifically targeted patient blood serum samples and complimentary age-matched controls, in parallel with the use of selected panels of these biomarkers, are being applied to the development of blood tests to specifically address unmet pressing needs in the differential diagnosis of these diseases, and to provide potential avenues for mechanism-based drug targeting and treatment monitoring. While exploring recent findings in this area, the review discusses differences in critical pathways of immune/inflammation and amyloid formation between Parkinson's disease and amyotrophic lateral sclerosis, as well as discernable synergistic relationships between these pathways that are revealed by this approach. The potential for pathway measurement in blood tests for differential diagnosis, disease burden and therapeutic monitoring is also outlined.
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Affiliation(s)
- Essam A Sheta
- Power3 Medical Products, Inc., The Woodlands, TX 77381, USA.
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17
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Lovett JE, Abbott RJM, Roversi P, Johnson S, Caesar JJE, Doria M, Jeschke G, Timmel CR, Lea SM. Investigating the structure of the factor B vWF-A domain/CD55 protein-protein complex using DEER spectroscopy: successes and pitfalls. Mol Phys 2013; 111:2865-2872. [PMID: 24954957 PMCID: PMC4056885 DOI: 10.1080/00268976.2013.827754] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 07/05/2013] [Indexed: 01/03/2023]
Abstract
The electron paramagnetic resonance technique of double electron-electron resonance (DEER) was used to measure nanometre-scale distances between nitroxide spin labels attached to the complement regulatory protein CD55 (also known as decay accelerating factor) and the von Willebrand factor A (vWF-A) domain of factor B. Following a thorough assessment of the quality of the data, distances obtained from good-quality measurements are compared to predicted distances from a previously hypothesised model for the complex and are found to be incompatible. The success of using these distances as restraints in multi-body docking routines is presented critically.
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Affiliation(s)
- Janet E Lovett
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK ; EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh, UK
| | - Rachel J M Abbott
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
| | - Pietro Roversi
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
| | - Steven Johnson
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
| | - Joseph J E Caesar
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK ; Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, University of Oxford, Oxford, UK
| | - Marianna Doria
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK ; Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, University of Oxford, Oxford, UK
| | - Gunnar Jeschke
- Laboratory for Physical Chemistry, ETH Zürich, Zürich, Switzerland
| | - Christiane R Timmel
- Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, University of Oxford, Oxford, UK
| | - Susan M Lea
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
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18
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Okroj M, Holmquist E, King BC, Blom AM. Functional analyses of complement convertases using C3 and C5-depleted sera. PLoS One 2012; 7:e47245. [PMID: 23071769 PMCID: PMC3468486 DOI: 10.1371/journal.pone.0047245] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Accepted: 09/11/2012] [Indexed: 01/30/2023] Open
Abstract
C3 and C5 convertases are central stages of the complement cascade since they converge the different initiation pathways, augment complement activation by an amplification loop and lead to a common terminal pathway resulting in the formation of the membrane attack complex. Several complement inhibitors attenuate convertase formation and/or accelerate dissociation of convertase complexes. Functional assays used to study these processes are often performed using purified complement components, from which enzymatic complexes are reconstituted on the surface of erythrocytes or artificial matrices. This strategy enables identification of individual interactions between convertase components and putative regulators but carries an inherent risk of detecting non-physiological interactions that would not occur in a milieu of whole serum. Here we describe a novel, alternative method based on C3 or C5-depleted sera, which support activation of the complement cascade up to the desired stages of convertases. This approach allows fast and simple assessment of the influence of putative regulators on convertase formation and stability. As an example of practical utility of the assay, we performed studies on thioredoxin-1 in order to clarify the mechanism of its influence on complement convertases.
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Affiliation(s)
- Marcin Okroj
- Department of Laboratory Medicine, Lund University, The Wallenberg Laboratory, Malmö, Sweden
| | - Emelie Holmquist
- Department of Laboratory Medicine, Lund University, The Wallenberg Laboratory, Malmö, Sweden
| | - Ben C. King
- Department of Laboratory Medicine, Lund University, The Wallenberg Laboratory, Malmö, Sweden
| | - Anna M. Blom
- Department of Laboratory Medicine, Lund University, The Wallenberg Laboratory, Malmö, Sweden
- * E-mail:
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19
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Microglia, Alzheimer's disease, and complement. Int J Alzheimers Dis 2012; 2012:983640. [PMID: 22957298 PMCID: PMC3432348 DOI: 10.1155/2012/983640] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Revised: 05/01/2012] [Accepted: 05/07/2012] [Indexed: 02/02/2023] Open
Abstract
Microglia, the immune cell of the brain, are implicated in cascades leading to neuronal loss and cognitive decline in Alzheimer's disease (AD). Recent genome-wide association studies have indicated a number of risk factors for the development of late-onset AD. Two of these risk factors are an altered immune response and polymorphisms in complement receptor 1. In view of these findings, we discuss how complement signalling in the AD brain and microglial responses in AD intersect. Dysregulation of the complement cascade, either by changes in receptor expression, enhanced activation of different complement pathways or imbalances between complement factor production and complement cascade inhibitors may all contribute to the involvement of complement in AD. Altered complement signalling may reduce the ability of microglia to phagocytose apoptotic cells and clear amyloid beta peptides, modulate the expression by microglia of complement components and receptors, promote complement factor production by plaque-associated cytokines derived from activated microglia and astrocytes, and disrupt complement inhibitor production. The evidence presented here indicates that microglia in AD are influenced by complement factors to adopt protective or harmful phenotypes and the challenge ahead lies in understanding how this can be manipulated to therapeutic advantage to treat late onset AD.
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20
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Complement activation as a biomarker for Alzheimer's disease. Immunobiology 2011; 217:204-15. [PMID: 21856034 DOI: 10.1016/j.imbio.2011.07.023] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2011] [Revised: 06/22/2011] [Accepted: 07/18/2011] [Indexed: 01/31/2023]
Abstract
There is increasing evidence from genetic, immunohistochemical, proteomic and epidemiological studies as well as in model systems that complement activation has an important role in the pathogenesis of Alzheimer's disease (AD). The complement cascade is an essential element of the innate immune response. In the brain complement proteins are integral components of amyloid plaques and complement activation occurs at the earliest stage of the disease. The complement cascade has been implicated as a protective mechanism in the clearance of amyloid, and in a causal role through chronic activation of the inflammatory response. In this review we discuss the potential for complement activation to act as a biomarker for AD at several stages in the disease process. An accurate biomarker that has sufficient predictive, diagnostic and prognostic value would provide a significant opportunity to develop and test for effective novel therapies in the treatment of AD.
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21
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Shanmugavelayudam SK, Rubenstein DA, Yin W. Effects of physiologically relevant dynamic shear stress on platelet complement activation. Platelets 2011; 22:602-10. [PMID: 21679034 DOI: 10.3109/09537104.2011.585257] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Disturbed shear stress, commonly found in cardiovascular diseases, plays important roles in platelet activation and functions. It has been reported that when activated by elevated shear stress, platelets were able to support complement activation to completion. In this study, through a dynamic cone and plate shearing device, three physiologically relevant shear stresses were applied to platelets, mimicking the shear conditions when platelets pass through a normal left coronary artery (0.05-1 Pa), a 60% stenosis (elevated shear stress at 6.5 Pa for less than 0.1 s), and when platelets are trapped in a recirculation zone past a stenosis (<0.5 Pa). After shear exposure, platelet-surface complement activation (C1q, C4d, iC3b, and SC5b-9 depositions) was measured using a solid-phase ELISA approach and flow cytometry. Production of complement regulatory proteins - C1-inhibitor (C1-INH) and complement receptor 1 (CR1), was also measured. Results demonstrated that low-pulsatile shear stress (recirculation) was able to initiate platelet complement activation, by increasing C1q deposition significantly. Both pathological shear stresses triggered significant increases in C1 inhibitor generation and noticeable changes in CR1 production, effectively preventing complement activation from completion. These results suggested that for platelets, low-pulsatile shear stress may be more pro-atherogenic, compared to elevated shear stress, especially when the shear stress exposure time is short.
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Abstract
Echovirus 7 (EV7) belongs to the Enterovirus genus within the family Picornaviridae. Many picornaviruses use IgG-like receptors that bind in the viral canyon and are required to initiate viral uncoating during infection. However, in addition, some of the enteroviruses use an alternative or additional receptor that binds outside the canyon. Decay-accelerating factor (DAF) has been identified as a cellular receptor for EV7. The crystal structure of EV7 has been determined to 3.1-Å resolution and used to interpret the 7.2-Å-resolution cryo-electron microscopy reconstruction of EV7 complexed with DAF. Each DAF binding site on EV7 is near a 2-fold icosahedral symmetry axis, which differs from the binding site of DAF on the surface of coxsackievirus B3, indicating that there are independent evolutionary processes by which DAF was selected as a picornavirus accessory receptor. This suggests that there is an advantage for these viruses to recognize DAF during the initial process of infection.
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Rodríguez de Córdoba S, Harris CL, Morgan BP, Llorca O. Lessons from functional and structural analyses of disease-associated genetic variants in the complement alternative pathway. Biochim Biophys Acta Mol Basis Dis 2010; 1812:12-22. [PMID: 20837143 DOI: 10.1016/j.bbadis.2010.09.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Revised: 09/03/2010] [Accepted: 09/07/2010] [Indexed: 11/15/2022]
Abstract
Complement is an essential component of innate immunity and a major trigger of inflammatory responses. A critical step in complement activation is the formation of the C3 convertase of the alternative pathway (AP), a labile bimolecular complex formed by activated fragments of the C3 and factor B components that is fundamental to provide exponential amplification of the initial complement trigger. Regulation of the AP C3 convertase is essential to maintain complement homeostasis in plasma and to protect host cells and tissues from damage by complement. During the last decade, several studies have associated genetic variations in components and regulators of the AP C3 convertase with a number of chronic inflammatory diseases and susceptibility to infection. The functional characterization of these protein variants has helped to decipher the critical pathogenic mechanisms involved in some of these complement related disorders. In addition, these functional data together with recent 3D structures of the AP C3 convertase have provided fundamental insights into the assembly, activation and regulation of the AP C3 convertase.
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Affiliation(s)
- Santiago Rodríguez de Córdoba
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, 28040 Madrid, Spain.
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24
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Torreira E, Tortajada A, Montes T, Rodríguez de Córdoba S, Llorca O. Coexistence of Closed and Open Conformations of Complement Factor B in the Alternative Pathway C3bB(Mg2+) Proconvertase. THE JOURNAL OF IMMUNOLOGY 2009; 183:7347-51. [DOI: 10.4049/jimmunol.0902310] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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25
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Hyperfunctional C3 convertase leads to complement deposition on endothelial cells and contributes to atypical hemolytic uremic syndrome. Blood 2009; 114:2837-45. [PMID: 19584399 DOI: 10.1182/blood-2009-01-197640] [Citation(s) in RCA: 122] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Complement is a major innate immune defense against pathogens, tightly regulated to prevent host tissue damage. Atypical hemolytic uremic syndrome (aHUS) is characterized by endothelial damage leading to renal failure and is highly associated with abnormal alternative pathway regulation. We characterized the functional consequences of 2 aHUS-associated mutations (D(254)G and K(325)N) in factor B, a key participant in the alternative C3 convertase. Mutant proteins formed high-affinity C3-binding site, leading to a hyperfunctional C3 convertase, resistant to decay by factor H. This led to enhanced complement deposition on the surface of alternative pathway activator cells. In contrast to native factor B, the 2 mutants bound to inactivated C3 and induced formation of functional C3-convertase on iC3b-coated surface. We demonstrated for the first time that factor B mutations lead to enhanced C3-fragment deposition on quiescent and adherent human glomerular cells (GEnCs) and human umbilical vein endothelial cells (HUVECs), together with the formation of sC5b-9 complexes. These results could explain the occurrence of the disease, since excessive complement deposition on endothelial cells is a central event in the pathogenesis of aHUS. Therefore, risk factors for aHUS are not only mutations leading to loss of regulation, but also mutations, resulting in hyperactive C3 convertase.
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26
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Janssen BJC, Gomes L, Koning RI, Svergun DI, Koster AJ, Fritzinger DC, Vogel CW, Gros P. Insights into complement convertase formation based on the structure of the factor B-cobra venom factor complex. EMBO J 2009; 28:2469-78. [PMID: 19574954 DOI: 10.1038/emboj.2009.184] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2009] [Accepted: 06/08/2009] [Indexed: 11/09/2022] Open
Abstract
Immune protection by the complement system critically depends on assembly of C3 convertases on the surface of pathogens and altered host cells. These short-lived protease complexes are formed through pro-convertases, which for the alternative pathway consist of the complement component C3b and the pro-enzyme factor B (FB). Here, we present the crystal structure at 2.2-A resolution, small-angle X-ray scattering and electron microscopy (EM) data of the pro-convertase formed by human FB and cobra venom factor (CVF), a potent homologue of C3b that generates more stable convertases. FB is loaded onto CVF through its pro-peptide Ba segment by specific contacts, which explain the specificity for the homologous C3b over the native C3 and inactive products iC3b and C3c. The protease segment Bb binds the carboxy terminus of CVF through the metal-ion dependent adhesion site of the Von Willebrand factor A-type domain. A possible dynamic equilibrium between a 'loading' and 'activation' state of the pro-convertase may explain the observed difference between the crystal structure of CVFB and the EM structure of C3bB. These insights into formation of convertases provide a basis for further development of complement therapeutics.
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Affiliation(s)
- Bert J C Janssen
- Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Department of Chemistry, Faculty of Science, Utrecht University, Utrecht, The Netherlands
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Wu J, Wu YQ, Ricklin D, Janssen BJC, Lambris JD, Gros P. Structure of complement fragment C3b-factor H and implications for host protection by complement regulators. Nat Immunol 2009; 10:728-33. [PMID: 19503104 PMCID: PMC2713992 DOI: 10.1038/ni.1755] [Citation(s) in RCA: 262] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Accepted: 05/14/2009] [Indexed: 01/28/2023]
Abstract
Factor H (FH) is an abundant regulator of complement activation and protects host cells from self-attack by complement. Here we provide insight into the regulatory activity of FH by solving the crystal structure of the first four domains of FH in complex with its target, complement fragment C3b. FH interacted with multiple domains of C3b, covering a large, extended surface area. The structure indicated that FH destabilizes the C3 convertase by competition and electrostatic repulsion and that FH enables proteolytic degradation of C3b by providing a binding platform for protease factor I while stabilizing the overall domain arrangement of C3b. Our results offer general models for complement regulation and provide structural explanations for disease-related mutations in the genes encoding both FH and C3b.
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Affiliation(s)
- Jin Wu
- Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Department of Chemistry, Utrecht University, Utrecht, The Netherlands
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28
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Structural and functional implications of the alternative complement pathway C3 convertase stabilized by a staphylococcal inhibitor. Nat Immunol 2009; 10:721-7. [PMID: 19503103 PMCID: PMC2729104 DOI: 10.1038/ni.1756] [Citation(s) in RCA: 175] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Accepted: 05/15/2009] [Indexed: 12/30/2022]
Abstract
Activation of the complement system generates potent chemoattractants and opsonizes cells for immune clearance. Short-lived protease complexes cleave complement component C3 into anaphylatoxin C3a and opsonin C3b. Here we report the crystal structure of the C3 convertase formed by C3b and the protease fragment Bb, which was stabilized by the bacterial immune-evasion protein SCIN. The data suggest that the proteolytic specificity and activity depends on dimerization of C3 with C3b of the convertase. SCIN blocked the formation of a productive enzyme-substrate complex. Irreversible dissociation of C3bBb is crucial to complement regulation and was determined by slow binding kinetics of the Mg2+-adhesion site in Bb. Understanding the mechanistic basis of the central complement activation step and microbial immune evasion strategies targeting this step will aid the development of complement therapeutics.
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Karnchanaphanurach P, Mirchev R, Ghiran I, Asara JM, Papahadjopoulos-Sternberg B, Nicholson-Weller A, Golan DE. C3b deposition on human erythrocytes induces the formation of a membrane skeleton-linked protein complex. J Clin Invest 2009; 119:788-801. [PMID: 19258706 DOI: 10.1172/jci36088] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Accepted: 01/07/2009] [Indexed: 11/17/2022] Open
Abstract
Decay-accelerating factor (DAF, also known as CD55), a glycosylphosphatidylinositol-linked (GPI-linked) plasma membrane protein, protects autologous cells from complement-mediated damage by inhibiting complement component 3 (C3) activation. An important physical property of GPI-anchored complement regulatory proteins such as DAF is their ability to translate laterally in the plasma membrane. Here, we used single-particle tracking and tether-pulling experiments to measure DAF lateral diffusion, lateral confinement, and membrane skeletal associations in human erythrocyte membranes. In native membranes, most DAF molecules exhibited Brownian lateral diffusion. Fluid-phase complement activation caused deposition of C3b, one of the products of C3 cleavage, onto erythrocyte glycophorin A (GPA). We then determined that DAF, C3b, GPA, and band 3 molecules were laterally immobilized in the membranes of complement-treated cells, and GPA was physically associated with the membrane skeleton. Mass spectrometry analysis further showed that band 3, alpha-spectrin, beta-spectrin, and ankyrin were present in a complex with C3b and GPA in complement-treated cells. C3b deposition was also associated with a substantial increase in erythrocyte membrane stiffness and/or viscosity. We therefore suggest that complement activation stimulates the formation of a membrane skeleton-linked DAF-C3b-GPA-band 3 complex on the erythrocyte surface. This complex may promote the removal of senescent erythrocytes from the circulation.
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Affiliation(s)
- Pallop Karnchanaphanurach
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02115, USA
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3D structure of the C3bB complex provides insights into the activation and regulation of the complement alternative pathway convertase. Proc Natl Acad Sci U S A 2009; 106:882-7. [PMID: 19136636 DOI: 10.1073/pnas.0810860106] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Generation of the alternative pathway C3-convertase, the central amplification enzyme of the complement cascade, initiates by the binding of factor B (fB) to C3b to form the proconvertase, C3bB. C3bB is subsequently cleaved by factor D (fD) at a single site in fB, producing Ba and Bb fragments. Ba dissociates from the complex, while Bb remains bound to C3b, forming the active alternative pathway convertase, C3bBb. Using single-particle electron microscopy we have determined the 3-dimensional structures of the C3bB and the C3bBb complexes at approximately 27A resolution. The C3bB structure shows that fB undergoes a dramatic conformational change upon binding to C3b. However, the C3b-bound fB structure was easily interpreted after independently fitting the atomic structures of the isolated Bb and Ba fragments. Interestingly, the divalent cation-binding site in the von Willebrand type A domain in Bb faces the C345C domain of C3b, whereas the serine-protease domain of Bb points outwards. The structure also shows that the Ba fragment interacts with C3b separately from Bb at the level of the alpha'NT and CUB domains. Within this conformation, the long and flexible linker between Bb and Ba is likely exposed and accessible for cleavage by fD to form the active convertase, C3bBb. The architecture of the C3bB and C3bBb complexes reveals that C3b could promote cleavage and activation of fB by actively displacing the Ba domain from the von Willebrand type A domain in free fB. These structures provide a structural basis to understand fundamental aspects of the activation and regulation of the alternative pathway C3-convertase.
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31
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Pienaar IS, Daniels WMU, Götz J. Neuroproteomics as a promising tool in Parkinson's disease research. J Neural Transm (Vienna) 2008; 115:1413-30. [PMID: 18523721 PMCID: PMC2862282 DOI: 10.1007/s00702-008-0070-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2008] [Accepted: 05/14/2008] [Indexed: 12/21/2022]
Abstract
Despite the vast number of studies on Parkinson's disease (PD), its effective diagnosis and treatment remains unsatisfactory. Hence, the relentless search for an optimal cure continues. The emergence of neuroproteomics, with its sophisticated techniques and non-biased ability to quantify proteins, provides a methodology with which to study the changes in neurons that are associated with neurodegeneration. Neuroproteomics is an emerging tool to establish disease-associated protein profiles, while also generating a greater understanding as to how these proteins interact and undergo post-translational modifications. Furthermore, due to the advances made in bioinformatics, insight is created concerning their functional characteristics. In this review, we first summarize the most prominent proteomics techniques and then discuss the major advances in the fast-growing field of neuroproteomics in PD. Ultimately, it is hoped that the application of this technology will lead towards a presymptomatic diagnosis of PD, and the identification of risk factors and new therapeutic targets at which pharmacological intervention can be aimed.
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Affiliation(s)
- Ilse S Pienaar
- Department of Medical Physiology, University of Stellenbosch, Matieland, South Africa.
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32
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Yin W, Ghebrehiwet B, Weksler B, Peerschke EIB. Regulated complement deposition on the surface of human endothelial cells: effect of tobacco smoke and shear stress. Thromb Res 2007; 122:221-8. [PMID: 18166221 DOI: 10.1016/j.thromres.2007.11.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 11/20/2007] [Accepted: 11/27/2007] [Indexed: 12/23/2022]
Abstract
Cigarette smoke and hemodynamic stress both contribute to vascular inflammation and associated atherosclerosis. We recently demonstrated direct activation of complement components C4 and C3 on human endothelial cells (EC). The present study was designed to explore complement activation on bone marrow microvascular endothelial cells (BMEC) and human umbilical vein endothelial cells (HUVEC) in response to endothelial cell injury by tobacco smoke extract, shear stress, or other known inflammatory and atherogenic mediators, lipopolysaccharide (LPS) and INF-gamma. Following treatment, confluent EC monolayers were exposed to plasma (60 min, 37 degrees C), and cell surface deposition of stable complement derivatives C4d, iC3b and SC5b-9 was measured in situ using an ELISA approach. Consistent with previous results, moderate levels of C4d, iC3b and SC5b-9 deposition were observed on native EC monolayers exposed to human plasma. Tobacco smoke and shear stress enhanced EC C4d deposition. In contrast, LPS and INF-gamma failed to affect EC mediated complement activation, despite evidence of EC activation illustrated by ICAM-1 expression. The combination of tobacco smoke and shear stress nearly doubled EC C4d expression. No increases in iC3b or SC5b-9 were noted, suggesting inhibition of classical and alternative pathway C3 convertase assembly or activity. Indeed, concomitantly increased surface expression of complement regulatory proteins CD35 (CR1) and CD55 was observed following EC exposure to tobacco smoke and shear stress. These results suggest that a balance between complement activation and regulation exists at the EC surface, and may impact vascular injury leading to thrombosis, arteriosclerosis, and atherogenesis.
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Affiliation(s)
- Wei Yin
- Department of Pathology and Laboratory of Medicine, Weill Medical College of Cornell University, New York, New York, USA
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33
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Sequence diversity of the Trypanosoma cruzi complement regulatory protein family. Infect Immun 2007; 76:750-8. [PMID: 18070905 DOI: 10.1128/iai.01104-07] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
As a central component of innate immunity, complement activation is a critical mechanism of containment and clearance of microbial pathogens in advance of the development of acquired immunity. Several pathogens restrict complement activation through the acquisition of host proteins that regulate complement activation or through the production of their own complement regulatory molecules (M. K. Liszewski, M. K. Leung, R. Hauhart, R. M. Buller, P. Bertram, X. Wang, A. M. Rosengard, G. J. Kotwal, and J. P. Atkinson, J. Immunol. 176:3725-3734, 2006; J. Lubinski, L. Wang, D. Mastellos, A. Sahu, J. D. Lambris, and H. M. Friedman, J. Exp. Med. 190:1637-1646, 1999). The infectious stage of the protozoan parasite Trypanosoma cruzi produces a surface-anchored complement regulatory protein (CRP) that functions to inhibit alternative and classical pathway complement activation (K. A. Norris, B. Bradt, N. R. Cooper, and M. So, J. Immunol. 147:2240-2247, 1991). This study addresses the genomic complexity of the T. cruzi CRP and its relationship to the T. cruzi supergene family comprising active trans-sialidase (TS) and TS-like proteins. The TS superfamily consists of several functionally distinct subfamilies that share a characteristic sialidase domain at their amino termini. These TS families include active TS, adhesions, CRPs, and proteins of unknown functions (G. A. Cross and G. B. Takle, Annu. Rev. Microbiol. 47:385-411, 1993). A sequence comparison search of GenBank using BLASTP revealed several full-length paralogs of CRP. These proteins share significant homology at their amino termini and a strong spatial conservation of cysteine residues. Alternative pathway complement regulation was confirmed for CRP paralogs with 58% (low) and 83% (high) identity to AAB49414. CRPs are functionally similar to the microbial and mammalian proteins that regulate complement activation. Sequence alignment of mammalian complement control proteins to CRP showed that these sequences are distinct, supporting a convergent evolutionary pathway. Finally, we show that a clonal line of T. cruzi expresses multiple unique copies of CRP that are differentially recognized by patient sera.
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34
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Harris CL, Pettigrew DM, Lea SM, Morgan BP. Decay-accelerating factor must bind both components of the complement alternative pathway C3 convertase to mediate efficient decay. THE JOURNAL OF IMMUNOLOGY 2007; 178:352-9. [PMID: 17182573 DOI: 10.4049/jimmunol.178.1.352] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Decay-accelerating factor (DAF; CD55) inhibits the complement (C) cascade by dissociating the multimolecular C3 convertase enzymes central to amplification. We have previously demonstrated using surface plasmon resonance (Biacore International) that DAF mediates decay of the alternative pathway C3 convertase, C3bBb, but not of the inactive proenzyme, C3bB, and have shown that the major site of interaction is with the larger cleavage subunit factor B (Bb) subunit. In this study, we dissect these interactions and demonstrate that the second short consensus repeat (SCR) domain of DAF (SCR2) interacts only with Bb, whereas SCR4 interacts with C3b. Despite earlier studies that found SCR3 to be critical to DAF activity, we find that SCR3 does not directly interact with either subunit. Furthermore, we demonstrate that properdin, a positive regulator of the alternative pathway, does not directly interact with DAF. Extending from studies of binding to decay-accelerating activity, we show that truncated forms of DAF consisting of SCRs 2 and 3 bind the convertase stably via SCR2-Bb interactions but have little functional activity. In contrast, an SCR34 construct mediates decay acceleration, presumably due to SCR4-C3b interactions demonstrated above, because SCR3 alone has no binding or functional effect. We propose that DAF interacts with C3bBb through major sites in SCR2 and SCR4. Binding to Bb via SCR2 increases avidity of binding, concentrating DAF on the active convertase, whereas more transient interactions through SCR4 with C3b directly mediate decay acceleration. These data provide new insights into the mechanisms involved in C3 convertase decay by DAF.
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Affiliation(s)
- Claire L Harris
- Department of Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Cardiff, United Kingdom
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35
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Milder FJ, Gomes L, Schouten A, Janssen BJC, Huizinga EG, Romijn RA, Hemrika W, Roos A, Daha MR, Gros P. Factor B structure provides insights into activation of the central protease of the complement system. Nat Struct Mol Biol 2007; 14:224-8. [PMID: 17310251 DOI: 10.1038/nsmb1210] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2006] [Accepted: 01/26/2007] [Indexed: 11/09/2022]
Abstract
Factor B is the central protease of the complement system of immune defense. Here, we present the crystal structure of human factor B at 2.3-A resolution, which reveals how the five-domain proenzyme is kept securely inactive. The canonical activation helix of the Von Willebrand factor A (VWA) domain is displaced by a helix from the preceding domain linker. The two helices conformationally link the scissile-activation peptide and the metal ion-dependent adhesion site required for binding of the ligand C3b. The data suggest that C3b binding displaces the three N-terminal control domains and reshuffles the two central helices. Reshuffling of the helices releases the scissile bond for final proteolytic activation and generates a new interface between the VWA domain and the serine protease domain. This allosteric mechanism is crucial for tight regulation of the complement-amplification step in the immune response.
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Affiliation(s)
- Fin J Milder
- Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Faculty of Sciences, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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36
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Janssen BJC, Gros P. Conformational complexity of complement component C3. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 586:291-312. [PMID: 16893080 DOI: 10.1007/0-387-34134-x_20] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Bert J C Janssen
- Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Dept. of Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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37
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de Jorge EG, Harris CL, Esparza-Gordillo J, Carreras L, Arranz EA, Garrido CA, López-Trascasa M, Sánchez-Corral P, Morgan BP, de Córdoba SR. Gain-of-function mutations in complement factor B are associated with atypical hemolytic uremic syndrome. Proc Natl Acad Sci U S A 2006; 104:240-5. [PMID: 17182750 PMCID: PMC1765442 DOI: 10.1073/pnas.0603420103] [Citation(s) in RCA: 340] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Hemolytic uremic syndrome (HUS) is an important cause of acute renal failure in children. Mutations in one or more genes encoding complement-regulatory proteins have been reported in approximately one-third of nondiarrheal, atypical HUS (aHUS) patients, suggesting a defect in the protection of cell surfaces against complement activation in susceptible individuals. Here, we identified a subgroup of aHUS patients showing persistent activation of the complement alternative pathway and found within this subgroup two families with mutations in the gene encoding factor B (BF), a zymogen that carries the catalytic site of the complement alternative pathway convertase (C3bBb). Functional analyses demonstrated that F286L and K323E aHUS-associated BF mutations are gain-of-function mutations that result in enhanced formation of the C3bBb convertase or increased resistance to inactivation by complement regulators. These data expand our understanding of the genetic factors conferring predisposition to aHUS, demonstrate the critical role of the alternative complement pathway in the pathogenesis of aHUS, and provide support for the use of complement-inhibition therapies to prevent or reduce tissue damage caused by dysregulated complement activation.
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Affiliation(s)
- Elena Goicoechea de Jorge
- *Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Claire L. Harris
- Department of Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Henry Wellcome Building, Heath Park, Cardiff CF14 4XN, United Kingdom
| | - Jorge Esparza-Gordillo
- *Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Luis Carreras
- Servicio de Nefrología, Hospital Universitario de Bellvitge, Feixa Llarga s/n 08907 Barcelona, Spain; and
| | - Elena Aller Arranz
- *Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | | | | | | | - B. Paul Morgan
- Department of Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Henry Wellcome Building, Heath Park, Cardiff CF14 4XN, United Kingdom
| | - Santiago Rodríguez de Córdoba
- *Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, 28040 Madrid, Spain
- To whom correspondence should be addressed. E-mail:
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38
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Liszewski MK, Leung MK, Hauhart R, Buller RML, Bertram P, Wang X, Rosengard AM, Kotwal GJ, Atkinson JP. Structure and regulatory profile of the monkeypox inhibitor of complement: comparison to homologs in vaccinia and variola and evidence for dimer formation. THE JOURNAL OF IMMUNOLOGY 2006; 176:3725-34. [PMID: 16517741 DOI: 10.4049/jimmunol.176.6.3725] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The outbreak of monkeypox in the Unites States in the summer of 2003 was the first occurrence of this smallpox-like disease outside of Africa. This limited human epidemic resulted from cross-infection of prairie dogs by imported African rodents. Although there were no human fatalities, this outbreak illustrates that monkeypox is an emerging natural infection and a potential biological weapon. We characterized a virulence factor expressed by monkeypox (monkeypox inhibitor of complement enzymes or MOPICE). We also compared its structure and regulatory function to homologous complement regulatory proteins of variola (SPICE) and vaccinia (VCP). In multiple expression systems, 5-30% of MOPICE, SPICE, and VCP consisted of function-enhancing disulfide-linked homodimers. Mammalian cells infected with vaccinia virus also expressed VCP dimers. MOPICE bound human C3b/C4b intermediate to that of SPICE and VCP. Cofactor activity of MOPICE was similar to VCP, but both were approximately 100-fold less efficient than SPICE. SPICE and VCP, but not MOPICE, possessed decay-accelerating activity for the C3 and C5 convertases of the classical pathway. Additionally, all three regulators possessed heparin-binding capability. These studies demonstrate that MOPICE regulates human complement and suggest that dimerization is a prominent feature of these virulence factors. Thus, our data add novel information relative to the functional repertoire of these poxviral virulence factors. Furthermore, targeting and neutralizing these complement regulatory active sites via mAbs is a therapeutic approach that may enhance protection against smallpox.
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Affiliation(s)
- M Kathryn Liszewski
- Department of Medicine/Division of Rheumatology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA
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39
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Kavanagh D, Kemp EJ, Richards A, Burgess RM, Mayland E, Goodship JA, Goodship THJ. Does complement factor B have a role in the pathogenesis of atypical HUS? Mol Immunol 2006; 43:856-9. [PMID: 16061287 DOI: 10.1016/j.molimm.2005.06.041] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2005] [Indexed: 11/28/2022]
Abstract
Atypical haemolytic uraemic syndrome (aHUS) is a disorder of complement dysregulation. Because complement factor B (fB) carries the catalytic site of the alternative pathway convertase we examined it as both a potential candidate gene and modifier in the pathogenesis of aHUS. No factor B gene (BF) mutations were found in 20 patients with aHUS. There was no statistical difference between controls and aHUS patients in either BF allele or haplotype frequency. In conclusion, in this small series of aHUS patients we found no evidence that fB has a major role in the pathogenesis of aHUS.
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Affiliation(s)
- David Kavanagh
- Washington University School of Medicine, Campus Box 8045, St. Louis, MO 63110, USA.
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40
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Goldknopf IL, Sheta EA, Bryson J, Folsom B, Wilson C, Duty J, Yen AA, Appel SH. Complement C3c and related protein biomarkers in amyotrophic lateral sclerosis and Parkinson's disease. Biochem Biophys Res Commun 2006; 342:1034-9. [PMID: 16516157 DOI: 10.1016/j.bbrc.2006.02.051] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Accepted: 02/09/2006] [Indexed: 11/19/2022]
Abstract
We have used quantitative 2D gel electrophoresis to analyze serum proteins from 422 patients with neurodegenerative diseases and normal individuals in an unbiased approach to identify biomarkers. Differences in abnormal serum levels were found between amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and related disorders for 34 protein biomarker spots, nine of which were related to the complement system. Of these nine, four spots originated from the Complement C3b-alpha-chain (C3c(1), C3c(2a), C3c(2b), and C3dg). The C3c spots (C3c(1), C3c(2a), and C3c(2b)) had the same amino acid sequence and glycosylation, though only C3c(1) was phosphorylated. In addition, Complement Factors H, Bb, and Pre-Serum amyloid protein displayed different serum concentrations in ALS, PD, and normal sera, whereas Complement C4b gamma-chain and Complement Factor I did not. The differential expression of the complement proteins provides potentially useful biomarkers as well as evidence for the involvement of inflammatory processes in the pathogenesis of ALS and PD.
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41
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Ciulla E, Emery A, Konz D, Krushkal J. Evolutionary history of orthopoxvirus proteins similar to human complement regulators. Gene 2005; 355:40-7. [PMID: 16023794 PMCID: PMC9628764 DOI: 10.1016/j.gene.2005.05.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2004] [Revised: 03/28/2005] [Accepted: 05/10/2005] [Indexed: 11/29/2022]
Abstract
Orthopoxviruses include many important pathogens such as variola major virus, camelpox, buffalopox, monkeypox, cowpox, and variola minor viruses. This group of viruses also includes vaccinia virus, which is extensively used in human vaccine development. Genomes of orthopoxviruses encode proteins with sequences similar to human regulators of complement activation (RCA) that contain tandem short consensus repeats (SCRs). We employed phylogenetic tree analysis to evaluate the structural relationships among SCRs of orthopoxvirus RCA-like proteins and those of human complement regulators. The human complement RCA proteins analyzed were factor H (FH), C4 binding protein alpha chain, membrane cofactor protein (MCP), decay accelerating factor (DAF), and complement receptors type 1 (CR1) and 2 (CR2). Sequences of key poxvirus regulators of complement activation, vaccinia virus complement control protein (VCP), smallpox inhibitor of complement enzymes (SPICE), and cowpox inflammation modulatory protein (IMP) were similar to SCRs 1 through 5 of C4 binding protein, alpha chain, and they were also clustered with other homologous repeats of MCP, DAF, CR1, CR2, and FH. Phylogenetic clustering of RCA sequences suggested that poxvirus complement regulators VCP, SPICE, and IMP arose from a single ancestral sequence that shared similarity with all human regulators of complement activation. Any changes in poxvirus complement regulators leading to the enhancement of their ability to regulate complement activation likely resulted from new mutations in the viral lineages.
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Affiliation(s)
- Emily Ciulla
- Department of Biology and Biotechnology, Worcester Polytechnic Institute, Worcester, MA, USA
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42
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Harris CL, Abbott RJM, Smith RA, Morgan BP, Lea SM. Molecular Dissection of Interactions between Components of the Alternative Pathway of Complement and Decay Accelerating Factor (CD55). J Biol Chem 2005; 280:2569-78. [PMID: 15536079 DOI: 10.1074/jbc.m410179200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The complement regulatory protein decay accelerating factor (DAF; CD55), inhibits the alternative complement pathway by accelerating decay of the convertase enzymes formed by C3b and factor B. We show, using surface plasmon resonance, that in the absence of Mg(2+), DAF binds C3b, factor B, and the Bb subunit with low affinity (K(D), 14 +/- 0.1, 44 +/- 10, and 20 +/- 7 microm, respectively). In the presence of Mg(2+), DAF bound Bb or the von Willebrand factor type A subunit of Bb with higher affinities (K(D), 1.3 +/- 0.5 and 2.2 +/- 0.1 microm, respectively). Interaction with the proenzyme C3bB was investigated by flowing factor B across a C3b-coated surface in the absence of factor D. The dissociation rate was dependent on the time of incubation, suggesting that a time-dependent conformational transition stabilized the C3b-factor B interaction. Activation by factor D (forming C3bBb) increased the complex half-life; however, the enzyme became susceptible to rapid decay by DAF, unlike the proenzyme, which was unaffected. A convertase assembled with cobra venom factor and Bb was decayed by DAF, albeit far less efficiently than C3bBb. DAF did not bind cobra venom factor, implying that Bb decay is accelerated, at least in part, through DAF binding of this subunit. It is likely that DAF binds the complex with higher affinity/avidity, promoting a conformational change in either or both subunits accelerating decay. Such analysis of component and regulator interactions will inform our understanding of inhibitory mechanisms and the ways in which regulatory proteins cooperate to control the complement cascade.
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Affiliation(s)
- Claire L Harris
- Complement Biology Group, Department of Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Heath Park, Cardiff, CF14 4XN, United Kingdom.
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Lukacik P, Roversi P, White J, Esser D, Smith GP, Billington J, Williams PA, Rudd PM, Wormald MR, Harvey DJ, Crispin MDM, Radcliffe CM, Dwek RA, Evans DJ, Morgan BP, Smith RAG, Lea SM. Complement regulation at the molecular level: the structure of decay-accelerating factor. Proc Natl Acad Sci U S A 2004; 101:1279-84. [PMID: 14734808 PMCID: PMC337044 DOI: 10.1073/pnas.0307200101] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2003] [Indexed: 11/18/2022] Open
Abstract
The human complement regulator CD55 is a key molecule protecting self-cells from complement-mediated lysis. X-ray diffraction and analytical ultracentrifugation data reveal a rod-like arrangement of four short consensus repeat (SCR) domains in both the crystal and solution. The stalk linking the four SCR domains to the glycosylphosphatidylinositol anchor is extended by the addition of 11 highly charged O-glycans and positions the domains an estimated 177 A above the membrane. Mutation mapping and hydrophobic potential analysis suggest that the interaction with the convertase, and thus complement regulation, depends on the burial of a hydrophobic patch centered on the linker between SCR domains 2 and 3.
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Affiliation(s)
- P Lukacik
- Laboratory of Molecular Biophysics and Glycobiology Institute, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, England
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Kuttner-Kondo LA, Dybvig MP, Mitchell LM, Muqim N, Atkinson JP, Medof ME, Hourcade DE. A Corresponding Tyrosine Residue in the C2/Factor B Type A Domain Is a Hot Spot in the Decay Acceleration of the Complement C3 Convertases. J Biol Chem 2003; 278:52386-91. [PMID: 14561755 DOI: 10.1074/jbc.m304620200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cleavage of C3 by the C3 convertases (C3bBb and C4b2a) determines whether complement activation proceeds. Dissociation (decay acceleration) of these central enzymes by the regulators decay-accelerating factor (DAF), complement receptor 1 (CR1), factor H, and C4-binding protein (C4BP) controls their function. In a previous investigation, we obtained evidence implicating the alpha4/5 region of the type A domain of Bb (especially Tyr338) in decay acceleration of C3bBb and proposed this site as a potential interaction point with DAF and long homologous repeat A of CR1. Because portions of only two DAF complement control protein domains (CCPs), CCP2 and CCP3, are necessary to mediate its decay of the CP C3 convertase (as opposed to portions of at least three CCPs in all other cases, e.g. CCPs 1-3 of CR1), DAF/C4b2a provides the simplest structural model for this reaction. Therefore, we examined the importance of the C2 alpha4/5 site on decay acceleration of C4b2a. Functional C4b2a complexes made with the C2 Y327A mutant, the C2 homolog to factor B Y338A, were highly resistant to DAF, C4BP, and long homologous repeat A of CR1, whereas C2 substitutions in two nearby residues (N324A and L328A) resulted in partial resistance. Our new findings indicate that the alpha4/5 region of C2a is critical to decay acceleration mediated by DAF, C4BP, and CR1 and suggest that decay acceleration of C4b2a and C3bBb requires interaction of the convertase alpha4/5 region with a CCP2/CCP3 site of DAF or structurally homologous sites of CR1 and C4BP.
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Affiliation(s)
- Lisa A Kuttner-Kondo
- Case Western Reserve University, Institute of Pathology, Cleveland, Ohio 44106, USA
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Wu R, Zhou M, Wang P. Adrenomedullin and adrenomedullin binding protein-1 downregulate TNF-alpha in macrophage cell line and rat Kupffer cells. REGULATORY PEPTIDES 2003; 112:19-26. [PMID: 12667621 DOI: 10.1016/s0167-0115(03)00018-1] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Recent studies have demonstrated that administration of adrenomedullin (AM) and AM binding protein-1 (AMBP-1) maintains cardiovascular stability and reduces mortality in sepsis. However, the mechanism responsible for the beneficial effect of AM/AMBP-1 remains unknown. The aim of this study therefore was to determine whether AM/AMBP-1 directly reduces lipopolysaccharide (LPS)-induced secretion of TNF-alpha from murine macrophage-like cell line RAW 264.7 cells and Kupffer cells isolated from normal rats. TNF-alpha release and gene expression were determined by ELISA and RT-PCR, respectively. The results indicated that LPS increased TNF-alpha production from RAW cells by 38-63-fold in a dose- and time-dependent manner. Although incubation with AM or AMBP-1 alone inhibited LPS-induced TNF-alpha release by 14-22% and 13-22%, respectively, AM and AMBP-1 in combination significantly suppressed TNF-alpha production (by 24-35%). Moreover, the upregulated TNF-alpha mRNA by LPS stimulation was significantly reduced by AM/AMBP-1, but not by AM or AMBP-1 alone. In the Kupffer cells primary culture, AM or AMBP-1 alone inhibited LPS-induced TNF-alpha production by 52% and 44%, respectively. Co-culture with AM/AMBP-1 markedly reduced TNF-alpha production (by 90%). Moreover, AM or AMBP-1 alone decreased TNF-alpha mRNA expression by 41% and 36%, respectively, whereas the combination of AM/AMBP-1 decreased its expression by 63%. These results indicate that AM and AMBP-1 in combination effectively suppress LPS-induced TNF-alpha expression and release especially from primary cultured Kupffer cells, suggesting that the downregulatory effect of AM/AMBP-1 on proinflammatory cytokine TNF-alpha may represent a mechanism responsible for their beneficial effects in preventing inflammatory responses and tissue damage in sepsis.
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Affiliation(s)
- Rongqian Wu
- Division of Surgical Research, Department of Surgery, North Shore-Long Island Jewish Medical Center and New York University School of Medicine, 350 Community Drive, Manhasset, NY 11030, USA
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Pandiripally V, Gregory E, Cue D. Acquisition of regulators of complement activation by Streptococcus pyogenes serotype M1. Infect Immun 2002; 70:6206-14. [PMID: 12379699 PMCID: PMC130388 DOI: 10.1128/iai.70.11.6206-6214.2002] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Opsonization of bacteria by complement proteins is an important component of the immune response. The pathogenic bacterium Streptococcus pyogenes has evolved multiple mechanisms for the evasion of complement-mediated opsonization. One mechanism involves the binding of human regulators of complement activation such as factor H (FH) and FH-like protein 1 (FHL-1). Acquisition of these regulatory proteins can limit deposition of the opsonin C3b on bacteria, thus decreasing the pathogen's susceptibility to phagocytosis. Binding of complement regulatory proteins by S. pyogenes has previously been attributed to the streptococcal M and M-like proteins. Here, we report that the S. pyogenes cell surface protein Fba can mediate binding of FH and FHL-1. We constructed mutant derivatives of S. pyogenes that lack Fba, M1 protein, or both proteins and assayed the strains for FH binding, susceptibility to phagocytosis, and C3 deposition. Fba expression was found to be sufficient for binding of purified FH as well as for binding of FH and FHL-1 from human plasma. Plasma adsorption experiments also revealed that M1(+) Fba(+) streptococci preferentially bind FHL-1, whereas M1(-) Fba(+) streptococci have similar affinities for FH and FHL-1. Fba was found to contribute to the survival of streptococci incubated with human blood and to inhibit C3 deposition on bacterial cells. Streptococci harvested from log-phase cultures readily bound FH, but binding was greatly reduced for bacteria obtained from stationary-phase cultures. Bacteria cultured in the presence of the protease inhibitor E64 maintained FH binding activity in stationary phase, suggesting that Fba is removed from the cell surface via proteolysis. Western analyses confirmed that E64 stabilizes cell surface expression of Fba. These data indicate that Fba is an antiopsonic, antiphagocytic protein that may be regulated by cell surface proteolysis.
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Affiliation(s)
- Vinod Pandiripally
- Department of Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
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