C4b-binding Protein Alpha-chain Research Articles

Targeted Blood Plasma Proteomics and Hemostasis Assessment of Post COVID-19 Patients with Acute Myocardial Infarction

The molecular mechanisms underlying cardiovascular complications after the SARS-CoV-2 infection remain unknown. The goal of our study was to analyze the features of blood coagulation, platelet aggregation, and plasma proteomics in COVID-19 convalescents with AMI. The study included 66 AMI patients and 58 healthy volunteers. The groups were divided according to the anti-N IgG levels (AMI post-COVID (n = 44), AMI control (n = 22), control post-COVID (n = 31), and control (n = 27)). All participants underwent rotational thromboelastometry, thrombodynamics, impedance aggregometry, and blood plasma proteomics analysis. Both AMI groups of patients demonstrated higher values of clot growth rates, thrombus size and density, as well as the elevated levels of components of the complement system, proteins modifying the state of endothelium, acute-phase and procoagulant proteins. In comparison with AMI control, AMI post-COVID patients demonstrated decreased levels of proteins connected to inflammation and hemostasis (lipopolysaccharide-binding protein, C4b-binding protein alpha-chain, plasma protease C1 inhibitor, fibrinogen beta-chain, vitamin K-dependent protein S), and altered correlations between inflammation and fibrinolysis. A new finding is that AMI post-COVID patients opposite the AMI control group, are characterized by a less noticeable growth of acute-phase proteins and hemostatic markers that could be explained by prolonged immune system alteration after COVID-19.

Proteomic analysis of small extracellular vesicles from the plasma of patients with hepatocellular carcinoma

PurposeLiver cancer is one of the most common tumors with the seventh-highest incidence and the third-highest mortality. Many studies have shown that small extracellular vesicles (sEVs) play an important role in liver cancer. Here, we report comprehensive signatures for sEV proteins from plasma obtained from patients with hepatocellular carcinoma (HCC), which might be valuable for the evaluation and diagnosis of HCC.MethodsWe extracted sEVs from the plasma of controls and patients with HCC. Differentially expressed proteins in the sEVs were analyzed using label-free quantification and bioinformatic analyses. Western blotting (WB) was used to validate the abovementioned sEV proteins.ResultsProteomic analysis was performed for plasma sEVs from 21 patients with HCC and 15 controls. Among the 335 identified proteins in our study, 27 were significantly dysregulated, including 13 upregulated proteins that were involved predominantly in the complement cascade (complement C1Q subcomponent subunit B (C1QB), complement C1Q subcomponent subunit C (C1QC), C4B-binding protein alpha chain (C4BPA), and C4B-binding protein beta chain (C4BPB)) and the coagulation cascade (F13B, fibrinogen alpha chain (FGA), fibrinogen beta chain (FGB), and fibrinogen gamma chain (FGG)). We verified increased levels of the C1QB, C1QC, C4BPA, and C4BPB proteins in the plasma sEVs from patients with HCC in both the discovery cohort and validation cohort.ConclusionsThe complement cascade in sEVs was significantly involved in HCC progression. C1QB, C1QC, C4BPA, and C4BPB were highly abundant in the plasma sEVs from patients with HCC and might represent molecular signatures.

Exosome Proteomics Reveals the Deregulation of Coagulation, Complement and Lipid Metabolism Proteins in Gestational Diabetes Mellitus.

Exosomes are small extracellular vesicles with a variable protein cargo in consonance with cell origin and pathophysiological conditions. Gestational diabetes mellitus (GDM) is characterized by different levels of chronic low-grade inflammation and vascular dysfunction; however, there are few data characterizing the serum exosomal protein cargo of GDM patients and associated signaling pathways. Eighteen pregnant women were enrolled in the study: 8 controls (CG) and 10 patients with GDM. Blood samples were collected from patients, for exosomes’ concentration. Protein abundance alterations were demonstrated by relative mass spectrometric analysis and their association with clinical parameters in GDM patients was performed using Pearson’s correlation analysis. The proteomics analysis revealed 78 significantly altered proteins when comparing GDM to CG, related to complement and coagulation cascades, platelet activation, prothrombotic factors and cholesterol metabolism. Down-regulation of Complement C3 (C3), Complement C5 (C5), C4-B (C4B), C4b-binding protein beta chain (C4BPB) and C4b-binding protein alpha chain (C4BPA), and up-regulation of C7, C9 and F12 were found in GDM. Our data indicated significant correlations between factors involved in the pathogenesis of GDM and clinical parameters that may improve the understanding of GDM pathophysiology. Data are available via ProteomeXchange with identifier PXD035673.

Abstract P4-07-17: Association between plasma-based sequential windowed acquisition mass spectrometry (SWATH-MS) and invasive disease free survival (iDFS) in HR+/HER2- early breast cancer in the CANTO cohort

Abstract Background: The definition of breast cancer (BC) prognosis has historically relied on clinico-pathological factors. Novel omics markers including proteomic analyses could improve our understanding of the biological host drivers of breast cancer recurrence and survival. We aimed at identifying patients (pts) at high risk of recurrence based on proteomic markers in plasma.Methods: CANTO is a multicenter, prospective cohort study of stage I-III BCS (NCT01993498). Plasma samples were collected on HR+/HER2- pts at diagnosis (dx) and analyzed by SWATH-MS, implemented by Biognosys AG (Schlieren, Switzerland), resulting in a relative quantification of the abundance of 500 proteins in the plasma. A Cox model was fitted to estimate to associate proteomic and clinical variables with the primary endpoint IDFS Clinical covariates consisted of age, stage and grade. An adaptive Lasso method was used to perform model selection. The discrimination performances of the model were assessed on 100 random train-test partitions of the cohort. Results: There were 457 pts with analyzed plasma samples. The median age at dx was 59.3 years, and the repartition of cancer stage was 52% for stage I, 37% for stage II and 11% for stage III. The mean duration of follow-up was 5.4 years, and 53 (11.5%) IDFS events (non local recurrences, second primary cancers and deaths) were reported. In total, 7 proteins were selected by the adaptive Lasso process; associated with the age, the stage and the grade at dx, 3 proteins were retained as having a significant impact on the IDFS: GTP-binding nuclear protein Ran (RAN), involved in cell division and GTP metabolic process, C4b-binding protein alpha-chain (C4BPA), involved in complement activation, and prothrombin (THRB), involved in acute-phase response and blood activation. Concordance indices were computed on 100 random test subsets of the cohort for the model with clinical variables only (0.67+/- 0.08), for the model with selected protein features only (0.74 +/- 0.07) and for the model with both proteomic and clinical covariates (0.75 +/-0.06). Conclusion: The discrimination performances of the estimated model suggest that proteomics provide relevant markers associated with BC prognosis. Validation on an independent validation set is required. Host related plasma proteins represent an avenue worth exploring to improve our understanding of BC relapse risk Table 1.Estimated hazard ratios of the linear Cox model.FeaturesHR* (95% CI)p-valuesRAN (for 1 SD increase)0.66 (0.51-0.85)<0.005THRB (for 1 SD increase)1.43 (0.99-2.06)0.05C4BPA (for 1 SD increase)1.44 (1.02-2.02)0.04stage--II vs I1.68 (0.82-3.46)0.16III vs I4.29 (1.88-9.75)<0.005HR = hazard ratio CI = confidence interval * adjusted by age and grade Citation Format: Antonin Della Noce, Stergios Christodoulidis, Antonio Di Meglio, Julie Havas, Alicia Tran-Dien, Fabrice André, Ines Vaz-Luis, Paul-Henry Cournède, Stefan Michiels. Association between plasma-based sequential windowed acquisition mass spectrometry (SWATH-MS) and invasive disease free survival (iDFS) in HR+/HER2- early breast cancer in the CANTO cohort [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-07-17.

Response of the critically endangered Przewalski's gazelle (Procapra przewalskii) to selenium deprived environment

Selenium (Se) is an essential mineral nutrient for animals. Se deprivation can lead to many disorders and even death. This study investigated the response of Przewalski's gazelle (P. przewalskii) to Se-deprived environment. We found that Se deprivation in soil and forage not only influenced the mineral contents of the blood and hair in P. przewalskii, but also severely disrupted their blood parameters. We identified significant changes in the abundance of 146 proteins and 25 metabolites (P < 0.05) in serum, including the selenoproteins L8IG93 (glutathione peroxidase) and F4YD09 (Cu/Zn superoxide dismutase). Furthermore, the major known proteins and metabolites associated with the Se stress response in P. przewalskii were Cu/Zn superoxide dismutase, the vitamin K-dependent protein C, the C4b-binding protein alpha chain, complement component C7, lipase linoleic acid, peptidase D, thymidine, pseudo-uridine, L-phenylalanine, L-glutamine, PGA1, and 15-deoxy-delta-12,14-PGJ2. The main signaling pathways involved included complement and coagulation cascades, metabolic pathways, and stress granule formation. Our results indicate that the intake of Se-deficient forage elicited an oxidative stress response in P. przewalskii. These findings provide insights into the response mechanisms of this threatened gazelle to Se stress, and enable the development of conservation strategies to protect populations on the Qinghai-Tibetan Plateau. SignificanceThis study is the first to point out the presence of oxidative stress in P. przewalskii in selenium-deficient areas through proteomics and metabolomics studies. These findings should prove helpful for conservation efforts aimed at P. przewalskii populations and maintenance of the integrity of their ecological environment.

Intracellular C4BPA Levels Regulate NF-κB-Dependent Apoptosis.

SummaryThe importance of innate immunity in cancer is increasingly being recognized with recent reports suggesting tumor cell-intrinsic intracellular functions for innate immunity proteins. However, such functions are often poorly understood, and it is unclear whether these are affected by patient-specific mutations. Here, we show that C4b-binding protein alpha chain (C4BPA), typically thought to reside in the extracellular space, is expressed intracellularly in cancer cells, where it interacts with the NF-κB family member RelA and regulates apoptosis. Interestingly, intracellular C4BPA expression is regulated in a stress- and mutation-dependent manner and C4BPA mutations are associated with improved cancer survival outcome. Using cell lines harboring patient-specific C4BPA mutations, we show that increasing intracellular C4BPA levels correlate with sensitivity to oxaliplatin-induced apoptosis in vitro and in vivo. Mechanistically, sensitive C4BPA mutants display increased IκBα expression and increased inhibitory IκBα-RelA complex stability. These data suggest a non-canonical intracellular role for C4BPA in regulating NF-κB-dependent apoptosis.

Effects of Caloric Restriction with Protein Supplementation on Plasma Protein Profiles in Middle-Aged Women with Metabolic Syndrome-A Preliminary Open Study.

Background: Clinical studies have demonstrated that higher protein intake based on caloric restriction (CR) alleviates metabolic abnormalities. However, no study has examined the effects of plasma protein profiles on caloric restriction with protein supplementation (CRPS) in metabolic syndrome (MetS). Therefore, using a proteomic perspective, this pilot study investigated whether CRPS ameliorated metabolic abnormalities associated with MetS in middle-aged women. Methods: Plasma samples of middle-aged women with MetS in CR (n = 7) and CRPS (n = 6) groups for a 12-week intervention were obtained and their protein profiles were analysed. Briefly, blood samples from qualified participants were drawn before and after the dietary treatment. Anthropometric, clinical, and biochemical variables were measured and correlated with plasma proteomics. Results: In results, we found that body mass index, total body fat, and fasting blood glucose decreased significantly after the interventions but were not different between the CR and CRPS groups. After liquid chromatography–tandem mass spectrometry analysis, the relative plasma levels of alpha-2-macroglobulin (A2M), C4b-binding protein alpha chain (C4BPA), complement C1r subcomponent-like protein (C1RL), complement component C6 (C6), complement component C8 gamma chain (C8G), and vitamin K-dependent protein S (PROS) were significantly different between the CRPS and CR groups. These proteins are involved in inflammation, the immune system, and coagulation responses. Moreover, blood low-density lipoprotein cholesterol levels were significantly and positively correlated with C6 plasma levels in both groups. Conclusions: These findings suggest that CRPS improves inflammatory responses in middle-aged women with MetS. Specific plasma protein expression (i.e., A2M, C4BPA, C1RL, C6, C8G, and PROS) associated with the complement system was highly correlated with fasting blood glucose (FBG), blood lipids (BLs), and body fat.

Characterization of serum proteins attached to distinct sol–gel hybrid surfaces

The success of a dental implant depends on its osseointegration, an important feature of the implant biocompatibility. In this study, two distinct sol-gel hybrid coating formulations [50% methyltrimethoxysilane: 50% 3-glycidoxypropyl-trimethoxysilane (50M50G) and 70% methyltrimethoxysilane with 30% tetraethyl orthosilicate (70M30T)] were applied onto titanium implants. To evaluate their osseointegration, in vitro and in vivo assays were performed. Cell proliferation and differentiation in vitro did not show any differences between the coatings. However, four and eight weeks after in vivo implantation, the fibrous capsule area surrounding 50M50G-implant was 10 and 4 times, respectively, bigger than the area of connective tissue surrounding the 70M30T treated implant. Thus, the in vitro results gave no prediction or explanation for the 50M50G-implant failure in vivo. We hypothesized that the first protein layer adhered to the surface may have direct implication in implant osseointegration, and perhaps correlate with the in vivo outcome. Human serum was used for adsorption analysis on the biomaterials, the first layer of serum proteins adhered to the implant surface was analyzed by proteomic analysis, using mass spectrometry (LC-MS/MS). From the 171 proteins identified; 30 proteins were significantly enriched on the 50M50G implant surface. This group comprised numerous proteins of the immune complement system, including several subcomponents of the C1 complement, complement factor H, C4b-binding protein alpha chain, complement C5 and C-reactive protein. This result suggests that these proteins enriched in 50M50G surface might trigger the cascade leading to the formation of the fibrous capsule observed. The implications of these results could open up future possibilities to predict the biocompatibility problems in vivo. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1477-1485, 2018.

Proteomic Analysis of Synovial Fluid Obtained From a Dog Diagnosed With Idiopathic Immune-Mediated Polyarthritis

This case study is to report the proteins detected by proteomic analysis of synovial fluid from a dog diagnosed with idiopathic immune-mediated polyarthritis, and to compare it with healthy dogs. Synovial fluid was collected via arthrocentesis from a dog diagnosed with immune-mediated polyarthritis. Protein precipitation was performed on the synovial fluid, followed by isoelectric focusing and 2-dimensional gel electrophoresis. The spots on the 2-dimensional gels were analyzed using MALDI-TOF/MS. The results were then analyzed against the MASCOT database. The results from the proteomic analysis revealed an abundance of several types of immunoglobulins together with the presence of complement C4b-binding protein alpha chain. Actin and keratin were also among the proteins detected. Proteomic studies, facilitate a better understanding of the different levels of proteins expressed during disease activity. Potential disease biomarkers can aid in the diagnosis of disease, as well as help in monitoring treatment efficacy and providing prognosis for the patient.

INDEED: Integrated differential expression and differential network analysis of omic data for biomarker discovery

Differential expression (DE) analysis is commonly used to identify biomarker candidates that have significant changes in their expression levels between distinct biological groups. One drawback of DE analysis is that it only considers the changes on single biomolecule level. Recently, differential network (DN) analysis has become popular due to its capability to measure the changes on biomolecular pair level. In DN analysis, network is typically built based on correlation and biomarker candidates are selected by investigating the network topology. However, correlation tends to generate over-complicated networks and the selection of biomarker candidates purely based on network topology ignores the changes on single biomolecule level. In this paper, we propose a novel approach, INDEED, that builds sparse differential network based on partial correlation and integrates DE and DN analyses for biomarker discovery. We applied this approach on real proteomic and glycomic data generated by liquid chromatography coupled with mass spectrometry for hepatocellular carcinoma (HCC) biomarker discovery study. For each omic data, we used one dataset to select biomarker candidates, built a disease classifier and evaluated the performance of the classifier on an independent dataset. The biomarker candidates, selected by INDEED, were more reproducible across independent datasets, and led to a higher classification accuracy in predicting HCC cases and cirrhotic controls compared with those selected by separate DE and DN analyses. INDEED also identified some candidates previously reported to be relevant to HCC, such as intercellular adhesion molecule 2 (ICAM2) and c4b-binding protein alpha chain (C4BPA), which were missed by both DE and DN analyses. In addition, we applied INDEED for survival time prediction based on transcriptomic data acquired by analysis of samples from breast cancer patients. We selected biomarker candidates and built a regression model for survival time prediction based on a gene expression dataset and patients’ survival records. We evaluated the performance of the regression model on an independent dataset. Compared with the biomarker candidates selected by DE and DN analyses, those selected through INDEED led to more accurate survival time prediction.

Proteomic analysis for the identification of serum diagnostic markers for joint hypermobility syndrome.

Joint hypermobility syndrome (JHS) (also termed Ehlers-Danlos syndrome, hypermobility type) is a heritable connective tissue disorder which is characterized by generalized joint hypermobility, chronic pain, dizziness, fatigue, and minor skin changes. However, it has yet to be determined in patients with JHS whether specific genetic factors are involved in the risk of developing the disorder. Therefore, interventions have been limited to symptomatic treatments, and biomarkers for diagnosis and therapy have not yet been identified. In the present study, to identify potential serum biomarkers for JHS, we examined proteins with differential levels in sera from patients with JHS and in sera from control individuals using isobaric tags for relative and absolute quantitation (iTRAQ) labeling in combination with nano LC-MALDI-TOF/TOF-MS/MS followed by ProteinPilot analysis. In the sera of patients with JHS, a total of 106 proteins with differential levels were identified, and they were further narrowed down to 6 proteins (p<0.05, patient vs. control). Of the 6 proteins, proteins involved in the complement system including complement C1r subcomponent (C1R), vitronectin (VTN), complement component C9 (C9), and C4b-binding protein alpha chain (C4BPA) were identified as increased proteins in sera from patients with JHS compared with those in sera from controls. We confirmed increased levels of C1R and VTN in sera from patients with JHS by western blot analyses. The results indicate the possibility of a locally occurring inflammatory process in patients with JHS.

Gray matter-related proteins are associated with childhood-onset multiple sclerosis.

Objective:To identify CSF biomarkers for multiple sclerosis (MS) in children with an initial acquired CNS demyelinating syndrome (ADS).Methods:CSF was collected from a cohort of 39 children with initial ADS, 18 of whom were diagnosed with MS and 21 of whom had a monophasic disease course. Proteomic analysis of trypsinized CSF (20 μL) was performed by nano-liquid chromatography Orbitrap mass spectrometry. Univariate statistical analysis was used to identify differentially abundant proteins between childhood-onset MS and monophasic ADS.Results:A total of 2,260 peptides corresponding to 318 proteins were identified in the total set of samples. Of these 2,260 peptides, 88 were identified as being most distinctive between MS and ADS. Fifty-three peptides, corresponding to 14 proteins, had higher abundance in children with MS compared to children with monophasic ADS. Twelve of these 14 proteins were linked to neuronal functions and structures, such as synapses, axons, and CNS proteases (e.g., neurofascin, carboxypeptidase E, brevican core protein, and contactin-2). The other 2 were functionally related to immune function. The 35 peptides identified with decreased abundance in children with MS corresponded to 7 proteins. Six of them were linked to innate immune function (e.g., haptoglobin, haptoglobin-related protein, C4b-binding protein alpha chain, and monocyte differentiation antigen CD14) and 1 was linked to cellular adhesion (protein diaphanous homolog 1).Conclusion:At first onset of ADS, CSF of children diagnosed with MS showed increased abundance of CNS gray matter–related proteins, whereas CSF of children with a monophasic disease course showed increased abundance of innate immunity–related proteins.

Yersinia pestis Ail recruitment of C4b-binding protein leads to factor I-mediated inactivation of covalently and noncovalently bound C4b.

The outer membrane protein Ail of Yersinia pestis mediates several virulence functions, including serum resistance. Here, we demonstrate that Ail binds C4b-binding protein (C4BP), the primary fluid-phase regulator of the classical and lectin pathways. Non-covalent binding of C4 and C4b to Ail was also observed. C4BP bound to Ail can act as a cofactor to the serine protease factor I (fI) in the cleavage of fluid-phase C4b. Employing a panel of C4BP alpha-chain mutants, we observed that the absence of complement control protein domain 6 and 8 reduced binding to Ail. Immunoblot analysis of normal human serum (NHS)-treated bacteria revealed minimal C4b alpha'-chain complexes with bacterial outer membrane targets. Addition of the anti-C4BP monoclonal antibody MK104 to NHS restored C4b-alpha' chain target complexes, suggesting that C4b binds covalently to targets on the Y. pestis surface. C4b bound to Ail noncovalently was also cleaved in a C4BP and fI-dependent manner, leaving the C4c fragment bound to Ail. MK104 also prevented the cleavage of noncovalently bound C4b. Collectively, these data suggest that when C4BP is bound to Ail, fI can cleave and inactivate C4b that has bound covalently to bacterial surface structures as well as C4b bound noncovalently to Ail.

Proteomics of inflammatory and oxidative stress response in cows with subclinical and clinical mastitis

Cow serum proteome was evaluated by three different complementary approaches in the control group, subclinical and clinical mastitis in order to possibly find differential protein expression useful for a better understanding of the pathophysiology of mastitis as well as for an early diagnosis of the disease. The systemic inflammatory and oxidative stress response in cows with subclinical and clinical mastitis were observed. The collected evidence shows a differential protein expression of serpin A3-1, vitronectin-like protein and complement factor H in subclinical mastitis in comparison with the control. It was also found a differential protein expression of inter-alpha-trypsin inhibitor heavy chain H4, serpin A3-1, C4b-binding protein alpha chain, haptoglobin and apolipoprotein A-I in clinical mastitis compared to the control. Among the inflammatory proteins up-regulated in clinical mastitis, vitronectin is over-expressed in both subclinical and clinical mastitis indicating a strong bacterial infection. This suggests vitronectin as an important mediator in the pathogenesis of the onset of mastitis as well as a valuable marker for diagnosis of the subclinical form of the disease. Obtained data could be useful for the detection of mastitis during the subclinical phase and for a better comprehension of the pathophysiological mechanisms involved in the onset of the disease.

Baseline Plasma Proteomic Analysis to Identify Biomarkers that Predict Radiation-Induced Lung Toxicity in Patients Receiving Radiation for Non-small Cell Lung Cancer

To identify new plasma proteomic markers before radiotherapy start to predict later grade ≥2 radiation-induced lung toxicity (RILT2). Fifty-seven patients with non-small cell lung cancer received radiotherapy (RT) were eligible. Forty-eight patients with minimum follow-up of 1 year, nine with RILT2 with tumor stage matched to 39 without RILT2, were enrolled for this analysis. Platelet-poor plasma was obtained within 2 weeks before radiotherapy. The plasma proteomes were compared using a multiplexed quantitative proteomics approach involving ExacTag labeling, reverse-phase high-performance liquid chromatography, and nano liquid chromatography electrospray ionization tandem mass spectrometry. Z scores and Bonferroni-adjusted p values for the two-sample mean comparison were used to identify the differential protein expression between patients with and without RILT2. More than 200 proteins were identified and quantified. After excluding proteins that were not detected in at least 40% of the 48 patient samples, C4b-binding protein alpha chain and vitronectin had significantly higher (p < 0.001 and p = 0.02) expression levels in patients with RILT2 compared with patients without RILT2. These two proteins were validated by Western blot. Ingenuity pathway analysis revealed that they both play important roles in the inflammatory response and are associated with the known pathways of radiation-induced lung damage. This proteomic approach demonstrates new plasma protein biomarkers before treatment for future studies on RILT2 prediction.

Plasma Proteomic Analysis May Identify New Markers for Radiation-Induced Lung Toxicity in Patients With Non–Small-Cell Lung Cancer

To study whether radiation induces differential changes in plasma proteomics in patients with and without radiation-induced lung toxicity (RILT) of Grade >/=2 (RILT2). A total of 57 patients with NSCLC received radiation therapy (RT) were eligible. Twenty patients, 6 with RILT2 with tumor stage matched to 14 without RILT2, were enrolled for this analysis. Platelet-poor plasma was obtained before RT, at 2, 4, 6 weeks during RT, and 1 and 3 months after RT. Plasma proteomes were compared using a multiplexed quantitative proteomics approach involving ExacTag labeling, reverse-phase high-performance liquid chromatography and nano-LC electrospray tandem mass spectrometry. Variance components models were used to identify the differential protein expression between patients with and without RILT2. More than 100 proteins were identified and quantified. After excluding proteins for which there were not at least 2 subjects with data for at least two time points, 76 proteins remained for this preliminary analysis. C4b-binding protein alpha chain, Complement C3, and Vitronectin had significantly higher expression levels in patients with RILT2 compared with patients without RILT2, based on both the data sets of RT start to 3 months post-RT (p < 0.01) and RT start to the end of RT (p < 0.01). The expression ratios of patients with RILT2 vs. without RILT2 were 1.60, 1.36, 1.46, and 1.66, 1.34, 1.46, for the above three proteins, respectively. This proteomic approach identified new plasma protein markers for future studies on RILT prediction.

Complement activation and plasma levels of C4b-binding protein in critical limb ischemia patients

Critical limb ischemia (CLI) is a peripheral arterial disease manifested by drastically diminished blood flow to the legs, pain at rest, nonhealing wounds, and gangrene caused by atherosclerosis. Significant tissue necrosis is associated with late stage CLI and the patients have a poor prognosis. Necrotic and apoptotic cells activate complement and bind complement inhibitor C4b-binding protein (C4BP). The major isoform of C4BP is composed of seven identical alpha-chains and one beta-chain, here termed C4BP(beta), whereas upon inflammation a normally less abundant isoform is upregulated that is exclusively composed of alpha-chains. Measuring the alpha-chains of C4BP includes both isoforms and is termed total C4BP (C4BP(tot)). The hypothesis of this study was that levels of complement activation and C4BP are predictive for the severity of the disease and that their measurement might be of clinical advantage. This was a prospective, single-center study of 259 consecutive patients with CLI admitted to a secondary referral center for vascular diseases. Interventions included evaluation of soluble terminal complement complexes (C5b-9), C4BP(tot) and C4BP(beta), lipid levels, the inflammatory mediators tumor necrosis factor-alpha, interleukin-6, 8-iso-prostaglandin F(2alpha), high-sensitivity C-reactive protein, neopterin, plasma homocysteine, and plasma endothelin-1 in plasma as well as resistance to activated protein C and ankle blood pressure. All data were compared with an age-matched population based control group of 219 currently healthy individuals. The data are presented as mean +/- SEM/median. CLI patients showed systemic complement activation (1.17 +/- 0.06/1.13 AU/mL vs 0.69 +/- 0.07/0.59 AU/mL in healthy controls, P < .0001), which was even higher in patients with gangrene (1.33 +/- 0.11/1.28 AU/mL vs 1.1 +/- 0.08/1.0 AU/mL, P = .0264), who also showed increased C4BP levels (421 +/- 28.6/386 microg/mL vs 341 +/- 10.8/318 microg/mL for C4BP(tot), P = .0248; 374 +/- 25.4/332 microg/mL vs 305 +/- 9.5/285 microg/mL for C4BP(beta), P = .0581). C4BP plasma levels were significantly elevated in CLI patients in comparison to healthy controls (351 +/- 8.1/322 microg/mL vs 297 +/- 8.0/288 microg/mL for C4BP(tot), P = .0001; 314 +/- 7.0/287 microg/mL vs 265 +/- 7.0/263 microg/mL for C4BP(beta), P = .0004) and correlated to levels of interleukin-6 (P(tot/beta) = .0048/.0019), high-sensitivity C-reactive protein (P < .0001), leukocyte (P(tot/beta) = .0086/.0043) and platelet count (P = .0001), LDL/HDL ratio (P(tot) = .0151) and HDL (P(tot/beta) = .0047/.0177), but not to tumor necrosis factor-alpha. Increased complement activation and C4BP plasma levels are related to the degree of tissue necrosis and disease severity of critical limb ischemia. This knowledge in combination with the found correlations to other biomarkers is useful for understanding the pathophysiology of the disease.

Cellular uptake of C4b‐binding protein is mediated by heparan sulfate proteoglycans and CD91/LDL receptor‐related protein

C4b-binding protein (C4BP) is a protein acting as a complement inhibitor and a carrier protein for anticoagulant protein S. Previously, we reported that the in vivo clearance of C4BP involves CD91, and that a CD91-interactive site overlaps the heparin-binding site within C4BP alpha-chains 26. Here, we investigated the C4BP-CD91 interaction in more detail. Binding of C4BP to CD91 was unaffected by protein S, which associates with C4BP beta-chain. Second, mutagenesis of cationic residues within C4BP alpha-chains impaired CD91 binding, reducing the affinity of triple mutant C4BPalpha/R39Q-R64Q-R66Q by 20-fold (Kd= 10 nM versus 214 nM for wild-type and mutant C4BP, respectively). Accordingly, intracellular degradation of this mutant by CD91-expressing cells was reduced to levels of CD91-deficient cells. Moreover, C4BPalpha/R39Q-R64Q-R66Q displayed a 3-fold prolonged survival compared to normal C4BP in in vivo clearance experiments. Since these residues also contribute to heparin binding, we explored the role of heparin-sulfate proteoglycans (HSPG) in the endocytosis of C4BP. The absence of HSPG was associated with a near complete absence of cell binding and intracellular degradation of C4BP. Apparently, the cellular uptake of C4BP depends on both HSPG and CD91, involving interactions with positively charged residues within C4BP alpha-chain.

The Complement Regulator C4b-Binding Protein (C4BP) Interacts with both the C4c and C4dg Subfragments of the Parent C4b Ligand: Evidence for Synergy in C4BP Subsite Binding

C4b-binding protein (C4BP) is a multimeric serum protein that is a potent regulator of the classical and lectin complement pathways. The binding site for C4b has been localized to complement control protein (CCP) domains 1-3 of the C4BP alpha-chain and, in particular, to a cluster of positively charged amino acids predicted to be at the interface between CCP 1 and CCP 2. To determine the regions of C4b contributing to C4BP binding, we have examined via surface plasmon resonance technology the binding of the C4c and C4dg subfragments of C4b to C4BP. At half-physiologic ionic strength, specific and saturable binding was observed for both C4c and C4dg. C4c exhibited much greater ionic strength sensitivity in its binding than did C4dg. Analysis of the effect on binding of the subfragments to various C4b-binding-defective C4BP mutants, together with cross-competition experiments, suggests that the subsites in C4BP for C4c and C4dg are adjacent, but distinct. Additionally, we observed synergy in subsite filling such that the presence of C4dg enhanced the extent of C4c binding over its basal level, and vice versa. The enhanced binding of C4c in the presence of C4dg was not due to an increase in affinity but rather reflected a 2-3-fold increase in the number of sites capable of binding C4c. This suggests the existence of a conformational equilibrium between high- and low-affinity states in the C4c binding subsite within each C4BP subunit, an equilibrium which is shifted in favor of the high-affinity state by the filling of the C4dg subsite.

A short consensus repeat-containing complement regulatory protein of lamprey that participates in cleavage of lamprey complement 3.

The prototype of the short consensus repeat (SCR)-containing C regulatory protein is of interest in view of its evolutionary significance with regard to the origin of the C regulatory system. Lamprey is an agnathan fish that belongs to the lowest class of vertebrates. Because it does not possess lymphocytes, it lacks Ig and consequently the classical C pathway. We identified an SCR-containing C regulatory protein from the lamprey. The primary structure predicted from the cDNA sequence showed that this is a secretary protein consisting of eight SCRs. This framework is similar to the alpha-chain of C4b-binding protein (C4bp). SCR2 and -3 of human C4bp are essential for C4b inactivation, and this region is fairly well conserved in the lamprey protein. However, the other SCRs of this protein are similar to those of other human C regulatory proteins. The lamprey protein binds to the previously reported lamprey C3b/C3bi deposited on yeast and cleaves lamprey C3b-like C3 together with a putative serum protease. The scheme resembles the C regulatory system of mammals, where factor I and its cofactor inactivate C3b. Unlike human cofactors, the lamprey protein requires divalent cations for C3b-like C3 cleavage. Its artificial membrane-anchored form protects host cells from lamprey C attack via the lectin pathway. Thus, the target of this protein appears to be C3b and/or its family. We named this protein Lacrep, the lamprey C regulatory protein. Lacrep is a member of SCR-containing C regulators, the first of its kind identified in the lowest vertebrates.