Complement regulator factor H in multiple sclerosis

A recent proteomic study published in this journal demonstrated lower cerebrospinal fluid (CSF) expression of factor H (fH), an important complement regulator, along with two other complement proteins, in active multiple sclerosis (MS) patients. We have previously demonstrated raised serum fH levels in MS and here, an extended analysis, quantifying fH in CSF, demonstrates no change in fH levels in active disease, but significantly raised levels in progressive disease. These findings support our previous work showing raised serum fH in patients with progressive MS, and our results predict that CSF fH levels will be raised rather than reduced in active disease.     

Sulfatide isoform pattern in cerebrospinal fluid discriminates progressive MS from relapsing‐remitting MS

Multiple sclerosis (MS ) is an inflammatory demyelinating disease of the central nervous system (CNS ). Several biomarkers including proteins and lipids have been reported in MS cerebrospinal fluid (CSF ), reflecting different aspects of the pathophysiology particularly of relapsing‐remitting MS (RRMS ). Sulfatide, abundant in the myelin sheath and a proposed target for autoimmune attack in MS , has been reported altered in MS CSF . Here, we investigated the potential of CSF sulfatide and its isoforms as biomarkers in MS . A highly sensitive and quantitative mass spectrometry method was employed to determine levels of sulfatide isoforms in CSF from RRMS and progressive MS (PMS ) patients, and healthy donors (HD ). We demonstrate that levels of total CSF sulfatide and C24:1, C26:1, and C26:1‐OH isoforms were significantly increased in PMS compared with RRMS patients and HD , while C23:0‐OH was significantly decreased in CSF from PMS patients compared to the other two groups. Multivariate discriminant analysis showed that CSF sulfatide isoform pattern in PMS patients was distinct and non‐overlapping with that of RRMS patients and HD . Sulfatide levels did not correlate with tested biomarkers or clinical parameters. The results suggest that CSF sulfatide isoform levels may be used to discriminate the phenotype of MS and might play a role in the progression of the disease.

     

Use of time-resolved FRET to validate crystal structure of complement regulatory complex between C3b and factor H (N terminus)

Structural knowledge of interactions amongst the ～ 40 proteins of the human complement system, which is central to immune surveillance and homeostasis, is expanding due primarily to X‐ray diffraction of co‐crystallized proteins. Orthogonal evidence, in solution, for the physiological relevance of such co‐crystal structures is valuable since intermolecular affinities are generally weak‐to‐medium and inter‐domain mobility may be important. In this current work, Förster resonance energy transfer (FRET) was used to investigate the 10 μM K_D (210 kD) complex between the N‐terminal region of the soluble complement regulator, factor H (FH1‐4), and the key activation‐specific complement fragment, C3b. Using site‐directed mutagenesis, seven cysteines were introduced individually at potentially informative positions within the four CCP modules comprising FH1‐4, then used for fluorophore attachment. C3b possesses a thioester domain featuring an internal cycloglutamyl cysteine thioester; upon hydrolysis this yields a free thiol (Cys988) that was also fluorescently tagged. Labeled proteins were functionally active as cofactors for cleavage of C3b to iC3b except for FH1‐4(Q40C) where conjugation with the fluorophore likely abrogated interaction with the protease, factor I. Time‐resolved FRET measurements were undertaken to explore interactions between FH1‐4 and C3b in fluid phase and under near‐physiological conditions. These experiments confirmed that, as in the cocrystal structure, FH1‐4 binds to C3b with CCP module 1 furthest from, and CCP module 4 closest to, the thioester domain, placing subsequent modules of FH near to any surface to which C3b is attached. The data do not rule out flexibility of the thioester domain relative to the remainder of the complex.     

Complement C3c and related protein biomarkers in amyotrophic lateral sclerosis and Parkinson's disease

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.     

Ubiquitin as potential cerebrospinal fluid marker of Creutzfeldt–Jakob disease

Until today, a definite diagnosis of Creutzfeldt–Jakob disease (CJD) can only be made neuropathologically. At lifetime the early and differential diagnosis is often a problem. With SELDI we analyzed cerebrospinal fluid (CSF) from 32 CJD patients, 32 patients having other dementive diseases and 31 non‐demented control subjects for diagnosis‐dependent protein pattern differences. In a screening set of patients, peaks that discriminate best between groups were identified. These peaks were subsequently analyzed using an independent validation set of patients. Diagnostic accuracies were compared with established markers like tau protein and 14‐3‐3‐protein. Potential marker proteins were purified and identified by LC‐MS/MS. In the validation set only one peak of 8.6 kDa out of ten in the screening set could be confirmed. This protein was identified to be ubiquitin and increased levels in CSF (but not in serum) of CJD patients were confirmed by Western blot. Ubiquitin allows the correct diagnoses of that CJD cases missed by tau protein or 14‐3‐3‐protein. We conclude that ubiquitin is a promising additional CSF biomarker for diagnosis of CJD, especially in differential diagnostically difficult cases. The selective increase of ubiquitin in CSF of CJD patients might point to an involvement of ubiquitin in pathophysiological process.     

Label‐free analysis of human cerebrospinal fluid addressing various normalization strategies and revealing protein groups affected by multiple sclerosis

The aims of the study were to: (i) identify differentially regulated proteins in cerebrospinal fluid (CSF) between multiple sclerosis (MS) patients and non‐MS controls; (ii) examine the effect of matching the CSF samples on either total protein amount or volume, and compare four protein normalization strategies for CSF protein quantification. CSF from MS patients (n = 37) and controls (n = 64), consisting of other noninflammatory neurological diseases (n = 50) and non neurological spinal anesthetic subjects (n = 14), were analyzed using label‐free proteomics, quantifying almost 800 proteins. In total, 122 proteins were significantly regulated (p < 0.05), where 77 proteins had p‐value <0.01 or AUC value >0.75. Hierarchical clustering indicated that there were two main groups of MS patients, those with increased levels of inflammatory response proteins and decreased levels of proteins involved in neuronal tissue development (n = 30), and those with normal protein levels for both of these protein groups (n = 7). The main subgroup of controls clustering with the MS patients showing increased inflammation and decreased neuronal tissue development were patients suffering from chronic fatigue. Our data indicate that the preferable way to quantify proteins in CSF is to first match the samples on total protein amount and then normalize the data based on the median intensities, preferably from the CNS‐enriched proteins.     

The overexpression of a single oncogene (ERBB2/HER2) alters the proteomic landscape of extracellular vesicles

ERBB2/HER2 amplification activates signaling cascades that lead to a tumor cell phenotype. However, despite its remarkable importance in oncology, the consequences of HER2 amplification over the extracellular vesicles (EVs) content have not yet been investigated. Here, we isolated EVs secreted by HB4a, a mammary luminal epithelial cell line and C5.2, its HER2‐overexpressing clone. We isolated two EV sets (20 and 100 K) by ultracentrifugation and used electron microscopy and nanoparticle tracking analysis for their morphological characterization. We employed GeLC‐MS/MS combined with isotope‐coded protein labeling to evaluate cell‐derived proteins and LC‐MS/MS label free spectral counting to quantify the EVs proteome. We found higher HER2 levels in both C5.2‐derived EVs when compared with C5.2 cells, suggesting its preferential shuttling. Proteins capable of inducing malignant transformation are enriched in both C5.2 EV subsets, including two HER2‐related proteins involved in cell motility and invasion, cofilin and CD44. MetaCore? analysis indicated an enrichment of cell adhesion and cytoskeleton‐remodeling pathways in C5.2 EVs, as well as proteins related to HER2 signaling, such as sphingosine‐1‐phosphate pathway. Together, our data indicate that in terms of protein content, distinct vesicle sets reinforce and complement each other. Our results also suggest that HER2‐upregulated proteins from EVs may be relevant for cellular malignancy and can be potential biomarkers for HER2⁺ cancer patients.     

Distinct localization of the complement C5b‐9 complex on Gram‐positive bacteria

The plasma proteins of the complement system fulfil important immune defence functions, including opsonization of bacteria for phagocytosis, generation of chemo‐attractants and direct bacterial killing via the Membrane Attack Complex (MAC or C5b‐9). The MAC is comprised of C5b, C6, C7, C8, and multiple copies of C9 that generate lytic pores in cellular membranes. Gram‐positive bacteria are protected from MAC‐dependent lysis by their thick peptidoglycan layer. Paradoxically, several Gram‐positive pathogens secrete small proteins that inhibit C5b‐9 formation. In this study, we found that complement activation on Gram‐positive bacteria in serum results in specific surface deposition of C5b‐9 complexes. Immunoblotting revealed that C9 occurs in both monomeric and polymeric (SDS‐stable) forms, indicating the presence of ring‐structured C5b‐9. Surprisingly, confocal microscopy demonstrated that C5b‐9 deposition occurs at specialized regions on the bacterial cell. On Streptococcus pyogenes, C5b‐9 deposits near the division septum whereas on Bacillus subtilis the complex is located at the poles. This is in contrast to C3b deposition, which occurs randomly on the bacterial surface. Altogether, these results show a previously unrecognized interaction between the C5b‐9 complex and Gram‐positive bacteria, whichmight ultimately lead to a new model of MAC assembly and functioning.     

Discovery and identification of serum potential biomarkers for pulmonary tuberculosis using iTRAQ‐coupled two‐dimensional LC‐MS/MS

Pulmonary tuberculosis (TB) caused by Mycobacterium tuberculosis is a chronic disease. Currently, there are no sufficiently validated biomarkers for early diagnosis of TB infection. In this study, a panel of potential serum biomarkers was identified between patients with pulmonary TB and healthy controls by using iTRAQ‐coupled 2D LC‐MS/MS technique. Among 100 differentially expressed proteins screened, 45 proteins were upregulated (>1.25‐fold at p < 0.05) and 55 proteins were downregulated (<0.8‐fold at p < 0.05) in the TB serum. Bioinformatics analysis revealed that the differentially expressed proteins were related to the response to stimulus, the metabolic and immune system processes. The significantly differential expression of apolipoprotein CII (APOCII), CD5 antigen‐like (CD5L), hyaluronan‐binding protein 2 (HABP2), and retinol‐binding protein 4 (RBP4) was further confirmed using immunoblotting and ELISA analysis. By forward stepwise multivariate regression analysis, a panel of serum biomarkers including APOCII, CD5L, and RBP4 was obtained to form the disease diagnostic model. The receiver operation characteristic curve of the diagnostic model was 0.98 (sensitivity = 93.42%, specificity = 92.86%). In conclusion, APOCII, CD5L, HABP2, and RBP4 may be potential protein biomarkers of pulmonary TB. Our research provides useful data for early diagnosis of TB.     

The Plasmodium falciparum blood stages acquire factor H family proteins to evade destruction by human complement

The acquisition of regulatory proteins is a means of blood‐borne pathogens to avoid destruction by the human complement. We recently showed that the gametes of the human malaria parasite Plasmodium falciparum bind factor H (FH) from the blood meal of the mosquito vector to assure successful sexual reproduction, which takes places in the mosquito midgut. While these findings provided a first glimpse of a complex mechanism used by Plasmodium to control the host immune attack, it is hitherto not known, how the pathogenic blood stages of the malaria parasite evade destruction by the human complement. We now show that the human complement system represents a severe threat for the replicating blood stages, particularly for the reinvading merozoites, with complement factor C3b accumulating on the surfaces of the intraerythrocytic schizonts as well as of free merozoites. C3b accumulation initiates terminal complement complex formation, in consequence resulting in blood stage lysis. To inactivate C3b, the parasites bind FH as well as related proteins FHL‐1 and CFHR‐1 to their surface, and FH binding is trypsin‐resistant. Schizonts acquire FH via two contact sites, which involve CCP modules 5 and 20. Blockage of FH‐mediated protection via anti‐FH antibodies results in significantly impaired blood stage replication, pointing to the plasmodial complement evasion machinery as a promising malaria vaccine target.     

Proteomics of rice and Cochliobolus miyabeanus fungal interaction: Insight into proteins at intracellular and extracellular spaces

Necrotrophic fungal pathogen Cochliobolus miyabeanus causes brown spot disease in rice leaves upon infection, resulting in critical rice yield loss. To better understand the rice–C. miyabeanus interaction, we employed proteomic approaches to establish differential proteomes of total and secreted proteins from the inoculated leaves. The 2DE approach after PEG‐fractionation of total proteins coupled with MS (MALDI‐TOF/TOF and nESI‐LC‐MS/MS) analyses led to identification of 49 unique proteins out of 63 differential spots. SDS‐PAGE in combination with nESI‐LC‐MS/MS shotgun approach was applied to identify secreted proteins in the leaf apoplast upon infection and resulted in cataloging of 501 unique proteins, of which 470 and 31 proteins were secreted from rice and C. miyabeanus, respectively. Proteins mapped onto metabolic pathways implied their reprogramming upon infection. The enzymes involved in Calvin cycle and glycolysis decreased in their protein abundance, whereas enzymes in the TCA cycle, amino acids, and ethylene biosynthesis increased. Differential proteomes also generated distribution of identified proteins in the intracellular and extracellular spaces, providing a better insight into defense responses of proteins in rice against C. miyabeanus. Established proteome of the rice–C. miyabeanus interaction serves not only as a good resource for the scientific community but also highlights its significance from biological aspects.     

Quantitative proteomics suggests decrease in the secretogranin‐1 cerebrospinal fluid levels during the disease course of multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the CNS with unknown cause. Proteins with different abundance in the cerebrospinal fluid (CSF) from relapsing‐remitting MS (RRMS) patients and neurological controls could give novel insight to the MS pathogenesis and be used to improve diagnosis, predict prognosis and disease course, and guide in therapy decisions. We combined iTRAQ labeling and Orbitrap mass spectrometry to discover proteins with different CSF abundance between six RRMS patients and 18 neurological disease controls. From 777 quantified proteins seven were selected as biomarker candidates, namely chitinase‐3‐like protein 1, secretogranin‐1 (Sg1), cerebellin‐1, neuroserpin, cell surface glycoprotein MUC18, testican‐2 and glutamate receptor 4. An independent sample set of 13 early‐MS patients, 13 RRMS patients and 13 neurological controls was used in a multiple reaction monitoring verification study. We found the intracellular calcium binding protein Sg1 to be increased in early‐MS patients compared to RRMS and neurological controls. Sg1 should be included in further studies to elucidate its role in the early phases of MS pathogenesis and its potential as a biomarker for this disease.     

The inhibition of covalent binding of the nascent complement component C4b to its target

The inhibition of covalent binding of the nascent C4b fragment of the human complement component to its natural target, immunoglobulin G, was studied. To this end, an immunoenzyme system was developed. In this ELISA method, the complement was activated on the sorbed IgG molecules and the resulting nascent C4b fragment acylated IgG or interacted with a competitive inhibitor added to the system. The inhibition constants for binding of the nascent C4b to its target were determined for immunoglobulins G1, G2, G3, G4, M, and A1, as well as for ferritin, yeast mannan, capsid polysaccharides of theNeisseria meningitidis A, B, and C serotypes, diphtheria anatoxin, epinephrine, and salicylic acid. On the basis of the experimental data, the immunoglobulin role at the activation stage of the complement regulation cascade, the relationship between the antigen immunogenicity and its ability to interact with C4b, and the direct effect of a number of therapeutic agents on the complement system were discussed. Lectins of various specificities were shown to inhibit the enzymic activation of C4 by the first complement component and the subsequent C4b sorption by its target, which allowed us to suggest that some oligosaccharide fragments of the C1s and C4 molecules are spatially close to the C1s active site and to the thioester bond of C4.     

Factor H-related protein 4 activates complement by serving as a platform for the assembly of alternative pathway C3 convertase via its interaction with C3b protein

Human complement factor H-related protein (CFHR) 4 belongs to the factor H family of plasma glycoproteins that are composed of short consensus repeat (SCR) domains. Although factor H is a well known inhibitor of the alternative complement pathway, the functions of the CFHR proteins are poorly understood. CFHR4 lacks SCRs homologous to the complement inhibitory domains of factor H and, accordingly, has no significant complement regulatory activities. We have previously shown that CFHR4 binds C-reactive protein via its most N-terminal SCR, which leads to classical complement pathway activation. CFHR4 binds C3b via its C terminus, but the significance of this interaction is unclear. Therefore, we set out to clarify the functional relevance of C3b binding by CFHR4. Here, we report a novel role for CFHR4 in the complement system. CFHR4 serves as a platform for the assembly of an alternative pathway C3 convertase by binding C3b. This is based on the sustained ability of CFHR4-bound C3b to bind factor B and properdin, leading to an active convertase that generates C3a and C3b from C3. The CFHR4-C3bBb convertase is less sensitive to the factor H-mediated decay compared with the C3bBb convertase. CFHR4 mutants containing exchanges of conserved residues within the C-terminal C3b-binding site showed significantly reduced C3b binding and alternative pathway complement activation. In conclusion, our results suggest that, in contrast to the complement inhibitor factor H, CFHR4 acts as an enhancer of opsonization by promoting complement activation.     

Ancient Origin of Human Complement Factor H

We studied the evolutionary history of two homologous proteins of the human complement system, factor H (FH) and the α chain of the C4b binding protein (C4bpα), and included in this study the related proteins from the barred sand bass (P. nebulifer) and the nematode C. elegans. Phylogenetic trees inferred from individual short consensus repeats (SCRs) and divergence among repeats from different genes suggest that human FH has a much closer evolutionary relationship to putative complement components from P. nebulifer and C. elegans than does the C4bpα. This indicates that a member of the alternative pathway of the complement system (FH) has an ancient origin, while a homologous member of the classical pathway (C4bpα) appeared later in evolutionary history as a result of gene duplication. The ancient evolutionary position of FH is in agreement with the suggestion that the alternative pathway of the complement system is older than the classical pathway. Phylogenetic analysis also shows that the sand bass cofactor protein SBP1 and cofactor related protein SBCRP-1 have diverged very recently. Received: 1 December 1997 / Accepted: 3 June 1998     

Intracerebral human regulatory T cells: analysis of CD4+ CD25+ FOXP3+ T cells in brain lesions and cerebrospinal fluid of multiple sclerosis patients

Impaired suppressive capacity of CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Treg) from peripheral blood of patients with multiple sclerosis (MS) has been reported by multiple laboratories. It is, however, currently unresolved whether Treg dysfunction in MS patients is limited to reduced control of peripheral T cell activation since most studies analyzed peripheral blood samples only. Here, we assessed early active MS lesions in brain biopsies obtained from 16 patients with MS by FOXP3 immunohistochemistry. In addition, we used six-color flow cytometry to determine numbers of Treg by analysis of FOXP3/CD127 expression in peripheral blood and cerebrospinal fluid (CSF) of 17 treatment-naïve MS patients as well as quantities of apoptosis sensitive CD45RO^hiCD95^hi cells in circulating and CSF Treg subsets. Absolute numbers of FOXP3⁺ and CD4⁺ cells were rather low in MS brain lesions and Treg were not detectable in 30% of MS biopsies despite the presence of CD4⁺ cell infiltrates. In contrast, Treg were detectable in all CSF samples and Treg with a CD45RO^hiCD95^hi phenotype previously shown to be highly apoptosis sensitive were found to be enriched in the CSF compared to peripheral blood of MS patients. We suggest a hypothetical model of intracerebral elimination of Treg by CD95L-mediated apoptosis within the MS lesion.     

Ail provides multiple mechanisms of serum resistance to Yersinia pestis

Ail, a multifunctional outer membrane protein of Yersinia pestis, confers cell binding, Yop delivery and serum resistance activities. Resistance to complement proteins in serum is critical for the survival of Y. pestis during the septicemic stage of plague infections. Bacteria employ a variety of tactics to evade the complement system, including recruitment of complement regulatory factors, such as factor H, C4b‐binding protein (C4BP) and vitronectin (Vn). Y. pestis Ail interacts with the regulatory factors Vn and C4BP, and Ail homologs from Y. enterocolitica and Y. pseudotuberculosis recruit factor H. Using co‐sedimentation assays, we demonstrate that two surface‐exposed amino acids, F80 and F130, are required for the interaction of Y. pestis Ail with Vn, factor H and C4BP. However, although Ail‐F80A/F130A fails to interact with these complement regulatory proteins, it still confers 10,000‐fold more serum resistance than a Δail strain and prevents C9 polymerization, potentially by directly interfering with MAC assembly. Using site‐directed mutagenesis, we further defined this additional mechanism of complement evasion conferred by Ail. Finally, we find that at Y. pestis concentrations reflective of early‐stage septicemic plague, Ail weakly recruits Vn and fails to recruit factor H, suggesting that this alternative mechanism of serum resistance may be essential during plague infection.     

A comprehensive proteome map of bovine cerebrospinal fluid

Cerebrospinal fluid (CSF) is considered as the most promising body fluid target for the discovery of biomarkers for early diagnosis of neurodegenerative diseases such as Creutzfeldt–Jakob disease in humans and bovine spongiform encephalopathy in cattle. For the recognition of disease‐associated changes in bovine CSF protein patterns, a detailed knowledge of this proteome is a prerequisite. The absence of a high‐resolution CSF proteome map prompted us to determine all bovine CSF protein spots that can be visualised on 2‐D protein gels. Using state‐of‐the‐art 2‐DE technology for proteome mapping of bovine ante mortem CSF combined with sensitive fluorescent protein staining and MALDI‐TOF/TOF MS for protein identification, a highly detailed 2‐DE map of the bovine CSF proteome was established. Besides the proteins mapped by earlier studies, this map contains 66 different proteins, including 58 which were not annotated in bovine 2‐DE CSF maps before.     

Involvement of Oxidative Stress in Occurrence of Relapses in Multiple Sclerosis: The Spectrum of Oxidatively Modified Serum Proteins Detected by Proteomics and Redox Proteomics Analysis

Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease of the central nervous system. Several evidences suggest that MS can be considered a multi-factorial disease in which both genetics and environmental factors are involved. Among proposed candidates, growing results support the involvement of oxidative stress (OS) in MS pathology. The aim of this study was to investigate the role of OS in event of exacerbations in MS on serum of relapsing-remitting (RR-MS) patients, either in relapsing or remitting phase, with respect to serum from healthy subjects. We applied proteomics and redox proteomics approaches to identify differently expressed and oxidatively modified proteins in the low-abundant serum protein fraction. Among differently expressed proteins ceruloplasmin, antithrombin III, clusterin, apolipoprotein E, and complement C3, were up-regulated in MS patients compared with healthy controls. Further by redox proteomics, vitamin D-binding protein showed a progressive trend of oxidation from remission to relapse, respect with controls. Similarly, the increase of oxidation of apolipoprotein A-IV confirmed that levels of OS are elevated with the progression of the disease. Our findings support the involvement of OS in MS and suggest that dysfunction of target proteins occurs upon oxidative damage and correlates with the pathology.