Complex C5b-9 Research Articles

Sublytic C5b-9 Complexes Induce Apoptosis of Glomerular Mesangial Cells in Rats with Thy-1 Nephritis through Role of Interferon Regulatory Factor-1-dependent Caspase 8 Activation

The apoptosis of glomerular mesangial cells (GMC) in rat Thy-1 nephritis (Thy-1N), a model of human mesangioproliferative glomerulonephritis, is accompanied by sublytic C5b-9 deposition, but the mechanism of sublytic C5b-9-mediated GMC apoptosis has not been elucidated. In the present study, the gene expression profiles both in the GMC stimulated by sublytic C5b-9 and the rat renal tissue of Thy-1N were detected using microarrays. Among the co-up-regulated genes, the up-regulation of interferon regulatory factor-1 (IRF-1) was further confirmed. Increased caspase 8 and caspase 3 expression and caspase 8 promoter activity in the GMC were also identified. Meanwhile, overexpression or knockdown of IRF-1 not only enhanced or inhibited GMC apoptosis and caspase 8 and 3 induction but also increased or decreased caspase 8 promoter activity, respectively. The element of IRF-1 binding to the caspase 8 promoter was first revealed. Furthermore, silencing IRF-1 or repressing the activation of caspases 8 and 3 significantly reduced GMC apoptosis, including other pathologic changes of Thy-1N. These novel findings indicate that GMC apoptosis of Thy-1N is associated with the IRF-1-activated caspase 8 pathway.

Neonatal Liver Cirrhosis Without Iron Overload Caused by Gestational Alloimmune Liver Disease

Gestational alloimmune liver disease has emerged as the major cause of antenatal liver injury and failure. It usually manifests as neonatal liver failure with hepatic and extrahepatic iron overload, a clinical presentation called neonatal hemochromatosis. We report on a newborn in whom fetal hepatomegaly was detected during pregnancy and who presented at birth with liver cirrhosis and mild liver dysfunction. Liver biopsy showed the absence of iron overload but strong immunostaining of hepatocytes for the C5b-9 complex, the terminal complement cascade neoantigen occurring specifically during complement activation by the immunoglobulin G-mediated classic pathway, which established the alloimmune nature of the hepatocyte injury. The infant survived with no specific therapy, and follow-up until 36 months showed progressive normalization of all liver parameters. This case report expands the recognized clinical spectrum of congenital alloimmune liver disease to include neonatal liver disease and cirrhosis, even in the absence of siderosis. Such a diagnosis is of utmost importance regarding the necessity for immunotherapy in further pregnancies to avoid recurrence of alloimmune injury.

Assembly and Regulation of the Membrane Attack Complex Based on Structures of C5b6 and sC5b9

Activation of the complement system results in formation of membrane attack complexes (MACs), pores that disrupt lipid bilayers and lyse bacteria and other pathogens. Here, we present the crystal structure of the first assembly intermediate, C5b6, together with a cryo-electron microscopy reconstruction of a soluble, regulated form of the pore, sC5b9. Cleavage of C5 to C5b results in marked conformational changes, distinct from those observed in the homologous C3-to-C3b transition. C6 captures this conformation, which is preserved in the larger sC5b9 assembly. Together with antibody labeling, these structures reveal that complement components associate through sideways alignment of the central MAC-perforin (MACPF) domains, resulting in a C5b6-C7-C8β-C8α-C9 arc. Soluble regulatory proteins below the arc indicate a potential dual mechanism in protection from pore formation. These results provide a structural framework for understanding MAC pore formation and regulation, processes important for fighting infections and preventing complement-mediated tissue damage.

Gestational alloimmune liver disease: a cause of fetal death in utero

Recent evidence suggests that neonatal haemochromatosis is caused by gestational alloimmune liver disease (GALD), and is an underdiagnosed entity, especially in cases of unexplained stillbirth or premature birth. 1 We present an autopsy case of a 35-year-old mother, G4P3, who was diagnosed with fetal death in utero (FDIU) at 32 weeks gestation. She had a previous child born with severe liver damage of unknown cause but suspected to be alloimmune. Her subsequent pregnancy was treated with immu-noglobulin and she delivered a normal child. This pregnancy immunoglobulin was not administered due to side-effects. At 32 weeks she noticed reduced fetal movements and FDIU was diagnosed. A full autopsy was performed which found features of terminal hypoxia, advanced liver autolysis, but no morphological abnormalities and negative Perls stain. Due to high clinical suspicion of neonatal haemochromatosis, liver autopsy samples and liver biopsy of child with severe hepatitis were sent to Children’s Memorial Research Centre, Chicago, for further analysis. Slides were stained with C5b-9 complex and were unequivocally positive in both liver biopsies. This is strong evidence that FDIU and severe hepatitis was due to GALD. Pathologists and clinicians need to be aware of GALD as a cause of FDIU.

Sublytic C5b‐9 complexes induce proliferative changes of glomerular mesangial cells in rat Thy‐1 nephritis through TRAF6‐mediated PI3K‐dependent Akt1 activation

The proliferation of glomerular mesangial cells (GMCs) and secretion of extracellular matrix (ECM) in rat Thy-1 nephritis (Thy-1N), resembling human mesangioproliferative glomerulonephritis (MsPGN), have been studied for many years, but the mechanisms, especially the role of signalling pathway activation and its regulation in GMCs triggered by sublytic C5b-9 complexes in Thy-1N rats remain largely unclear. In the study, the proliferation of GMCs and production of ECM as well as the role of PI3K/Akt and its regulation, both in GMCs induced by sublytic C5b-9 (in vitro) and in the renal tissues of rats with Thy-1N (in vivo), were determined and the results revealed that GMCs proliferation and ECM secretion, both in vitro and in vivo, were notably increased, and that PI3K/Akt1 activation and its regulation, such as TNF receptor-associated factor 6 (TRAF6)-mediated Akt1 ubiquitination and PI3K-dependent Akt1 phosphorylation, were involved in the process of Thy-1N induction. On the other hand, silence of the TRAF6, PI3K or Akt1 genes could obviously diminish the proliferative damages and urinary protein secretion of Thy-1N rats. Together, these data implicated that sublytic C5b-9 complexes in Thy-1N rats could promote GMCs proliferation and ECM production through TRAF6-mediated PI3K-dependent Akt1 activation, in which the ubiquitination and phosphorylation of the Akt1 signal molecule played an important role in the initiation and development of the proliferative changes in the rats with Thy-1N.

English

The complement system plays a strategic role in the vertebrate immune system in protecting the host from infection by numerous pathogenic agents. The system consists of at least 30 proteins that orchestrate attack on pathogenic agents. Although the susceptibility of Gram-negative bacteria to complement attack has been under investigation for over 100 years, the mechanism(s) by which the complement directly kills Gram-negative bacteria (Escherichia coli J5) is not understood. Inner membrane damage to E. coli J5 by complement with the subsequent release of cytoplasmic and periplasmic markers are important for killing. That observation has been extended to show that complement attack on Gram-negative bacteria prevents the detoxification of methylglyoxal, a lethal by-product of glucose metabolism. It is very important to know that lysozyme is not required for killing by C5b-9 complexes. That is, C5b-9 complexes kill bacteria but lysis of the organisms do not occur in lysozyme depleted or lysozyme neutralized serum. Killing is a function of damage or injury to the cytoplasmic membrane in E. coli J5 by C5b-9 complexes with the subsequent accumulation of a toxic by-product (methylgloxal) from glucose metabolism. Key words: Complement proteins, Gram-negative bacteria, cytoplasmic membrane, methylglyoxal.

Gestational Alloimmune Liver Disease in Cases of Fetal Death

To determine whether alloimmune liver disease can be identified as a cause of fetal death. This is a retrospective examination of the autopsy tissue of 6 stillborn fetuses and 2 extreme preterm infants (gestational age, 20 to 34 weeks) drawn from families referred for suspected neonatal hemochromatosis. Thirteen appropriate nondisease controls and 8 cases of neonatal acute liver failure with known etiology were also examined. Liver sections were immunostained using anti-human C5b-9 complex. All of the study cases had died with no preceding evidence of fetal distress. Histopathology showed findings of acute liver injury, including global hepatocyte necrosis with minimal reticulum collapse and no fibrosis. Hepatocytes in cases stained strongly positively for C5b-9 complex, suggesting premortem lgG complement-mediated liver injury. Hepatocytes in acute liver failure case controls did not demonstrate a similar mechanism of liver injury. Alloimmune liver disease is sometimes associated with fetal death.

Atherosclerosis and complement: anaphylatoxin C5a as a new risk marker and therapeutic target

The complement cascade is activated within atherosclerotic plaques Activation of the complement system is a major aspect of many chronic inflammatory diseases. Thus, it is not surprising that several lines of evidence suggest that the complement system may also be involved in the pathogenesis of athero sclerosis. The complement system consists of several inactive zymogens that, upon activation, assemble with other components and are converted into active proteases or effector compounds. The complement cascade can be divided into the following three sequential steps: initiation of complement activation by the classical, alternative or the lectin pathway; complement amplification by activation of C3 and C5 convertases; and the effector functions of the terminal pathway, consisting of the terminal complement complex (TCC) C5b-9 and the proinflammatory anaphylatoxins C3a and C5a. A major activator of the classical complement pathway within atherosclerotic plaques is C-reactive protein (CRP) whose effects are pronounced after binding to enzymatically modified LDL, oxidized LDL or apoptotic cells. The classical pathway may also be activated by autoantibodies against oxidized LDL and against heat shock proteins. The alternative pathway is activated by enzymatically modified LDL, apoptotic cells and cellular debris, as well as free cholesterol crystals that can be found within the necrotic core of an atherosclerotic lesion. In addition, Chlamydia pneumoniae may contribute to complement activation by the lectin pathway and coagulation factors could directly activate C3 and C5. Normal arterial intima is free from activated complement; however, when fatty streaks are formed in cholesterol-fed rabbits, complement

Activating transcription factor 3 promotes sublytic C5b-9-induced glomerular mesangial cells apoptosis through up-regulation of Gadd45α and KLF6 (44.5)

Abstract The sublytic C5b-9 complexes can result in glomerular mesangial cells (GMCs) apoptosis, which involved in the initiation and development of rat Thy-1 nephritis, but the mechanism of sublytic C5b-9-mediated GMCs apoptosis remains unclear. Activating transcription factor 3 (ATF3) is an immediate early gene for cells to cope with a variety of stress signals, and our previous study revealed that ATF3 could promote GMCs apoptosis attacked by sublytic C5b-9. However, target genes of ATF3 in GMCs apoptosis triggered by sublytic C5b-9 stimulation have not been identified. In this study, the data showed that the expression of ATF3, growth arrest and DNA damage-45 alpha (Gadd45α), Krüppel-like factor 6 (KLF6) and proliferating cell nuclear antigen (PCNA) in the GMCs induced by sublytic C5b-9 for the indicated time was significantly increased, and ATF3 expression could lead to GMCs apoptosis through up-regulation of Gadd45α and KLF6, but not up-regulation of PCNA. Furthermore, Gadd45α was identified as a downstream target gene regulated by ATF3 directly, and KLF6 might be regulated by ATF3 in an indirect manner.

Activating transcription factor 3 (ATF3) promotes sublytic C5b-9-induced glomerular mesangial cells apoptosis through up-regulation of Gadd45α and KLF6 gene expression

The sublytic C5b-9 complexes can result in glomerular mesangial cells (GMCs) apoptosis, which involved in the initiation and development of rat Thy-1 nephritis. Activating transcription factor 3 (ATF3) is an immediate early gene for cells to cope with a variety of stress signals, and our previous study revealed that ATF3 could promote GMCs apoptosis attacked by sublytic C5b-9. But the mechanism of ATF3 promoting GMCs apoptosis triggered by sublytic C5b-9 attack has not been elucidated. In this study, the data showed that the expression of ATF3, growth arrest and DNA damage-45 alpha (Gadd45α), Krüppel-like factor 6 (KLF6) and proliferating cell nuclear antigen (PCNA) in the GMCs in response to sublytic C5b-9 stimulation for the indicated time was significantly increased, and ATF3 expression could lead to GMCs apoptosis through up-regulation of Gadd45α and KLF6, but not up-regulation of PCNA. Furthermore, Gadd45α was identified as a downstream target gene regulated by ATF3 directly, and KLF6 might be regulated by ATF3 in an indirect manner.

Complement alternative pathway acts as a positive feedback amplification of neutrophil activation

AbstractComplement alternative pathway plays an important, but not clearly understood, role in neutrophil-mediated diseases. We here show that neutrophils themselves activate complement when stimulated by cytokines or coagulation-derived factors. In whole blood, tumor necrosis factor/formyl-methionyl-leucyl-phenylalanine or phorbol myristate acetate resulted in C3 fragments binding on neutrophils and monocytes, but not on T cells. Neutrophils, stimulated by tumor necrosis factor, triggered the alternative pathway on their surface in normal and C2-depleted, but not in factor B-depleted serum and on incubation with purified C3, factors B and D. This occurred independently of neutrophil proteases, oxidants, or apoptosis. Neutrophil-secreted properdin was detected on the cell surface and could focus “in situ” the alternative pathway activation. Importantly, complement, in turn, led to further activation of neutrophils, with enhanced CD11b expression and oxidative burst. Complement-induced neutrophil activation involved mostly C5a and possibly C5b-9 complexes, detected on tumor necrosis factor- and serum-activated neutrophils. In conclusion, neutrophil stimulation by cytokines results in an unusual activation of autologous complement by healthy cells. This triggers a new amplification loop in physiologic innate immunity: Neutrophils activate the alternative complement pathway and release C5 fragments, which further amplify neutrophil proinflammatory responses. This mechanism, possibly required for effective host defense, may be relevant to complement involvement in neutrophil-mediated diseases.

Role of activating transcription factor 3 (ATF3) in sublytic C5b‐9‐induced glomerular mesangial cell apoptosis

Sublytic complement C5b-9 complexes can cause cell apoptosis, but the mechanism of glomerular mesangial cell (GMC) apoptosis mediated by these complexes has not been well defined. The activating transcription factor 3 (ATF3) gene is an immediate early gene for the cell to cope with a variety of stress signals and can promote apoptosis of some cells. In this study, ATF3 expression and cell apoptosis in GMCs induced by sublytic C5b-9 were measured, and then the effects of ATF3 gene over-expression or knockdown on GMC apoptosis induced by sublytic C5b-9 were examined at a fixed time. The results showed that both ATF3 expression and GMC apoptosis were markedly increased and ATF3 over-expression obviously increased sublytic C5b-9-induced GMC apoptosis, whereas ATF3 gene silencing had a significant opposite effect. Collectively, these findings indicate that upregulation of ATF3 gene expression is involved in regulating GMC apoptosis induced by sublytic C5b-9 complexes.

Novel Mechanism of Fetal Hepatocyte Injury in Congenital Alloimmune Hepatitis Involves the Terminal Complement Cascade

Evidence suggests that most neonatal hemochromatosis (NH) is the phenotypic expression of gestational alloimmune fetal liver injury. Gestational alloimmune diseases are induced by the placental passage of specific reactive immunoglobulin G and often involve the activation of fetal complement by the classical pathway leading to the formation of membrane attack complex (MAC) as the effector of cell injury. We examined liver specimens from cases of NH, from cases of non-NH liver disease, and from infants without liver disease to determine if they would provide evidence that MAC is involved in hepatocyte injury. Sections were immunostained with anti-human C5b-9 complex, the terminal complement cascade (TCC) neoantigen formed in the assembly of MAC. Fetal liver injury in NH cases is associated with a severe loss of hepatocytes. In all NH cases examined, most remaining hepatocytes showed intense staining for TCC neoantigen, whereas hepatocytes in non-NH liver disease cases showed variable light staining. The percentage of hepatocytes containing TCC neoantigen in NH was much greater than that in non-NH liver disease, and there was no overlap between the groups. Findings in both groups suggest that hepatocytes have mechanisms to protect against MAC, including a biliary pathway for its excretion. The finding that all cases of proven NH contained TCC neoantigen far in excess of cases of other neonatal liver diseases suggests that a single process, namely congenital alloimmune hepatitis, is the principal cause of NH. MAC-mediated alloimmune injury in congenital alloimmune hepatitis is a novel mechanism of liver injury that results from an interplay of maternal adaptive immunity and fetal innate immunity.

Apoptosis of glomerular mesangial cells induced by sublytic C5b‐9 complexes in rats with Thy‐1 nephritis is dependent on Gadd45γ upregulation

The complement C5b-9 complexes can result in cell apoptosis, but the mechanism of sublytic C5b-9-mediated glomerular mesangial cell (GMC) apoptosis in Thy-1 nephritis (Thy-1N) remains largely unclear. The Gadd45 gene is involved in the cellular response to DNA damage and can promote cell apoptosis. In this study, both Gadd45 gamma expression patterns and pathologic changes of renal tissue were examined in rat Thy-1N. Both Gadd45 gamma expression and GMC apoptosis were significantly decreased in Thy-1N rats upon the depletion of complement with cobra venom factor. Our in vitro studies showed that Gadd45 gamma over-expression increased sublytic C5b-9-induced GMC apoptosis, while Gadd45 gamma gene knockdown by siRNA greatly reduced GMC apoptosis. Moreover, Gadd45 gamma gene silencing in vivo markedly inhibited the pathologic changes in the renal tissue of Thy-1N rats. These data suggest that Gadd45 gamma gene expression is involved in regulating GMC apoptosis mediated by sublytic C5b-9 in Thy-1N.

The down-stream effects of mannan-induced lectin complement pathway activation depend quantitatively on alternative pathway amplification

Complement activation plays an important role in human pathophysiology. The effect of classical pathway activation is largely dependent on alternative pathway (AP) amplification, whereas the role of AP for the down-stream effect of mannan-induced lectin pathway (LP) activation is poorly understood. In normal human serum specific activation of LP was obtained after exposure to a wide concentration range of mannan on the solid phase. Reaction mechanisms in this system were delineated in inhibition experiments with monoclonal antibodies.Direct mannose-binding lectin (MBL) independent activation of AP was not observed even at high mannan concentrations since addition of the inhibiting anti-MBL mAb 3F8 completely abolished generation of the terminal C5b-9 complex (TCC). However, selective blockade of AP by anti-factor D inhibited more than 80% of TCC release into the fluid phase after LP activation showing that AP amplification is quantitatively responsible for the final effect of initial specific LP activation. TCC generation on the solid phase was distinctly but less inhibited by anti-fD. C2 bypass of the LP pathway could be demonstrated, and AP amplification was also essential during C2 bypass in LP as shown by complete inhibition of TCC generation in C2-deficient serum by anti-fD and anti-properdin antibodies. In conclusion, the down-stream effect of LP activation depends strongly on AP amplification in normal human serum and in the C2 bypass pathway.

Preclinical evaluation of innate immunity to baculovirus gene therapy vectors in whole human blood

Interactions of gene therapy vectors with human blood components upon intravenous administration have a significant effect on vector efficacy and patient safety. Here we describe methods to evaluate these interactions and their effects in whole human blood, using baculovirus vectors as a model. Opsonisation of baculovirus particles by binding of IgM and C3b was demonstrated, which is likely to be the cause of the significant blood cell-associated virus that was detected. Preventing formation of the complement C5b-9 (membrane attack) complex maintained infectivity of baculovirus particles as shown by studying the effects of two specific complement inhibitors, Compstatin and a C5a receptor antagonist. Formation of macroscopic blood clots after 4h was prevented by both complement inhibitors. Pro- and anti-inflammatory cytokines Il-1β, IL-6, IL-8 and TNF-α were produced at variable levels between volunteers and complement inhibitors showed patient-specific effects on cytokine levels. Whilst both complement inhibitors could play a role in protecting patients from aggressive inflammatory reactions, only Compstatin maintained virus infectivity. We conclude that this ex vivo model, used here for the first time with infectious agents, is a valuable tool in evaluating human innate immune responses to gene therapy vectors or to predict the response of individual patients as part of a clinical trial or treatment. The use of complement inhibitors for therapeutic viruses should be considered on a patient-specific basis.

Complement: Alive and Kicking Nanomedicines

Administration of liposome- and polymer-based clinical nanomedicines, as well as many other proposed multifunctional nanoparticles, often triggers hypersensitivity reactions without the involvement of IgE. These anaphylactic reactions are believed to be secondary to activation of the complement system, giving rise to the release of anaphylatoxins C3a and C5a that initiate a wide array of responses through their effect on mast cells, polymorphonuclear cells, platelets and monocytes. Additionally, the terminal complement C5b-9 complex induces platelet activation, thereby enhancing their procoagulant activity, and has the capacity to elicit non-lytic stimulatory responses from vascular endothelial cells. Here we discuss the molecular basis of complement activation by liposomes, including poly(ethylene glycol) coated vesicles, and other related lipid-based and phospholipid-poly(ethylene glycol) conjugate stabilized entities. We have further considered the role of these complement activating entities in experimental oncology since intra-tumoural complement activation is suggested to induce tumour growth and progression.

Effects of PI3-k/Akt short hairpin RNA on proliferation, fibronectin production and synthesis of thrombospondin-1 and transforming growth factor-beta1 in glomerular mesangial cells induced by sublytic C5b-9 complexes.

To explore proliferation of glomerular mesangial cells (GMC) and secretion of extracellular matrix (fibronectin induced by sublytic C5b-9 complexes), and then ascertain the role of phosphatidylinositol 3-kinase (PI3-k)/Akt signal pathway in these processes, by using small hairpin RNAs. The expression of cyclin D(2), (3)H-thymidine into DNA and production of fibronectin including thrombospondin-1 and transforming growth factor-beta(1) in the GMCs stimulated by sublytic C5b-9 or transfected with expression vectors of PI3-k and Akt short hairpin RNA or LY294002 (PI3-k inhibitor) were measured by Real-time quantitative polymerase chain reaction (PCR), Western blot, enzyme-linked immunosorbent assay (ELISA) and (3)H-thymidine incorporation ((3)H-TdR), respectively. The expression of cyclin D(2), (3)H-thymidine into DNA and fibronectin in the GMCs stimulated by sublytic C5b-9 could all be increased, and the elevations of these parameters mentioned above were also markedly reduced in the GMCs transfected with vectors of PI3-k and Akt short hairpin RNA or LY294002, respectively. These data indicate that sublytic C5b-9 can promote proliferation of GMCs and secretion of fibronectin as well as synthesis of thrombospondin-1 and transforming growth factor-beta(1). The PI3-k/Akt signal pathway in these reactions, mediated by sublytic C5b-9 complexes, may play at least a partial role.

Quantitative measurement of SC5b-9 and C5b-9(m) in infarcted areas of human myocardium

Previous immunohistochemical work has indicated that terminal C5b-9 complement complexes are selectively deposited in infarcted areas of human myocardium. In the present study, we sought to quantify C5b-9 levels in myocardial tissue, and to differentiate between the membrane-bound C5b-9 (m) and the cytolytically inactive SC5b-9 complex. Paired tissue specimens from infarcted and non-infarcted myocardium were obtained from 36 autopsies. The homogenized and washed tissues were extracted with n-octyl-beta-D-glucopyranoside (octylglucoside) detergent, and the concentrations of C5b-9 in the extracts were determined by ELISA. Membrane-derived C5b-9 (m) and SC5b-9 were differentiated from each other on the basis of their characteristic sedimentation behaviour in sucrose density gradients. It was found that infarcted myocardial tissue contained on average an approximately three-fold higher concentration of C5b-9, compared with non-infarcted tissue. This increase was due in part to an increase in levels of C5b-9 (m). The results corroborate previous immunohistochemical data and show that complement activation occurs to completion with the generation of potentially cytotoxic C5b-9 complexes in infarcted myocardial tissues.

The Deposition of C5b-9 Complexes and Its Precursors on E. coli J5 During Complement Activation Enhances Uptake and Toxicities of Gentamicin

The complement system provides the host with protection against pathogenic agents and in some cases can result in damage to host tissue. However, the exact mechanism of how complement kills gram-negative bacteria in lysozyme-neutralized and or lysozyme-depleted serum is still under active investigation. In previous studies, it has been demonstrated that inner membrane damage by the membrane attack complex contributes to depolarization and the subsequent collapse of the membrane potential. In these studies we have shown that the membrane attack complex and its precursors provide additional protective effect by the enhanced uptake of antibiotics in the death of E. coli J5. Specifically, the deposition of C5b fragments from C6 neutralized Pooled Normal Human Serum (PNHS) and C5b6 complexes from C7 neutralized PNHS on E. coli J5 contribute to antibiotic uptake and killing. Since C5b and C5b6 do not form pores, we suggest that disturbances and or cracks in the outer membrane by the deposited complexes accelerates uptake of the antibiotics and enhanced killing of E. coli J5 employed in these studies.