Beta2-glycoprotein I and its clinical significance: from gene sequence to protein levels

Dysregulation of Lipid Metabolism Serves as A Link Between Alzheimer's and Cardiovascular Disease, As Witnessed in A Cross-Sectional Study

Cardiovascular risk factors and established cardiovascular disease (CVD) increase the risk of suffering dementia of the Alzheimer's type (DAT). Here, we set out to define specific molecular profiles of CVD in patients with DAT to better understand its relationship, to unravel the mechanisms underlying the high risk of developing DAT in CVD patients and to define new markers of early disease. Plasma samples from patients with DAT, with and without CVD, were analyzed through a multiomics approach, with integration of metabolomics and proteomics datasets using the OmicsNet web-based tool. Metabolomics results showed an enrichment in lipids and lipid-like molecules. Similarly, the most significant cluster identified through proteomics was formed by 5 proteins related to lipoprotein and cholesterol metabolism. After integration and functional enrichment, glycerolipid metabolism, fatty acid degradation and sphingolipid metabolism were among the most significant functions. Finally, differential expression of ABCA1 and APOH proteins was verified, in an independent cohort also including controls and patients with CVD alone. Both proteins positively correlated with phospho-Tau (181), a classical hallmark of DAT. Different molecular profiles exist in patients with DAT, with and without CVD, with exacerbated alterations in patients in which DAT and CVD co-exist. This information may help to define biomarkers like ABCA1 and APOH that identify patients with cardiovascular dysfunction that are at high risk of developing DAT. Such markers will allow more personalized interventions to be selected, a further step towards precision medicine for individuals whose molecular profiles indicate a distinct response to the same management strategies.

Identification of Potential Drug Targets for Antiplatelet Therapy Specifically Targeting Platelets of Old Individuals through Proteomic Analysis

Aging is a growing problem worldwide, and the prevalence and mortality of arterial and venous thromboembolism (VTE) are higher in the elderly than in the young population. To address this issue, various anticoagulants have been used. However, no evidence can confirm that antithrombotic agents are suitable for the elderly. Therefore, this study aims to investigate the platelet proteome of aged mice and identify antithrombotic drug targets specific to the elderly. Based on the proteome analysis of platelets from aged mice, 308 increased or decreased proteins were identified. Among these proteins, three targets were selected as potential antithrombotic drug targets. These targets are membrane proteins or related to platelet function and include beta-2-glycoprotein 1 (β2GP1, ApolipoproteinH (ApoH)), alpha-1-acid glycoprotein2 (AGP2, Orosomucoid-2 (Orm2)), and Ras-related protein (Rab11a).

Genetic risk factors in thrombotic primary antiphospholipid syndrome: A systematic review with bioinformatic analyses

BACKGROUND

Antiphospholipid Syndrome (APS) is an autoimmune multifactorial disorder. Genetics is believed to play a contributory role in the pathogenesis of APS, especially in thrombosis development and pregnancy morbidity. In the last 20 years, extensive research on genetic contribution on APS indicates that APS is a polygenic disorder, where a number of genes are involved in the development of its clinical manifestations.

AIMS

The aim of this systematic review is to evaluate the genetic risk factors in thrombotic primary APS. Additionally, to assess the common molecular functions, biological processes, pathways, interrelations with the gene encoded proteins and RNA-Seq-derived expression patterns over different organs of the associated genes via bioinformatic analyses.

METHODS

Without restricting the year, a systematic search of English articles was conducted (up to 4th September 2017) using Web of Science, PubMed, Scopus, ScienceDirect and Google Scholar databases. Eligible studies were selected based on the inclusion criteria. Two researchers independently extracted the data from the included studies. Quality assessment of the included studies was carried out using a modified New-Castle Ottawa scale (NOS).

RESULTS

From an initial search result of 2673 articles, 22 studies were included (1268 primary APS patients and 1649 healthy controls). Twenty-two genes were identified in which 16 were significantly associated with thrombosis in primary APS whereas six genes showed no significant association with thrombosis. Based on the NOS, 14 studies were of high quality while 6 were low quality studies. From the bioinformatic analyses, thrombin-activated receptor activity (q = 6.77 × 10^-7), blood coagulation (q = 2.63 × 10^-15), formation of fibrin clot (q = 9.76 × 10^-10) were the top hit for molecular function, biological process and pathway categories, respectively. With the highest confidence interaction score of 0.900, all of the thrombosis-associated gene encoded proteins of APS were found to be interconnected except for two. Based on the pathway analysis, cumulatively all the genes affect haemostasis [false discovery rate (FDR) = 1.01 × 10^-8] and the immune system [FDR = 9.93 × 10^-2]. Gene expression analysis from RNA-Seq data revealed that almost all the genes were expressed in 32 different tissues in the human body.

CONCLUSION

According to our systematic review, 16 genes contribute significantly in patients with thrombotic primary APS when compared with controls. Bioinformatic analyses of these genes revealed their molecular interconnectivity in protein levels largely by affecting blood coagulation and immune system. These genes are expressed in 32 different organs and may pose higher risk of developing thrombosis anywhere in the body of primary APS patients.

Diminished expression of β2-GPI is associated with a reduced ability to mitigate complement activation in anti-GPIIb/IIIa-mediated immune thrombocytopenia

Anti-GPIIb/IIIa-mediated complement activation has been reported to be important in the pathogenesis of immune thrombocytopenia (ITP). However, the role of the complement system and the involved regulatory mechanism remain equivocal. Beta2-glycoprotein I (β2-GPI), known as the main target for antiphospholipid autoantibodies, has been demonstrated as a complement regulator. Here, we investigated the complement-regulatory role of β2-GPI in anti-GPIIb/IIIa-mediated ITP. Plasma complement activation and enhanced complement activation capacity (CAC) were found in ITP patients with anti-GPIIb/IIIa antibodies in vivo and in vitro. Diminished plasma levels of β2-GPI were shown in patients of this group, which was inversely correlated with C5b-9 deposition. C5b-9 generation was inhibited by approximate physiological concentrations of β2-GPI, in a dose-dependent manner. Inhibition of C3a generation by β2-GPI and the existence of β2-GPI/C3 complexes in plasma indicated a regulation on the level of the C3 convertase. Furthermore, β2-GPI down-regulated the phosphorylation levels of c-Jun N-terminal kinase (JNK) and cleavage of BH3 interacting domain death agonist (Bid) and ultimately harbored platelet lysis. Our findings may provide a novel link between diminished plasma levels of β2-GPI and enhanced complement activation, indicating β2-GPI as a potential diagnostic biomarker and therapeutic target in the treatment of anti-GPIIb/IIIa-mediated ITP.

Genome-wide significant results identified for plasma apolipoprotein H levels in middle-aged and older adults

Apolipoprotein H (ApoH) is a multi-functional plasma glycoprotein that has been associated with negative health outcomes. ApoH levels have high heritability. We undertook a genome-wide association study of ApoH levels using the largest sample to date and replicated the results in an independent cohort (total N = 1,255). In the discovery phase, a meta-analysis of two cohorts, the Sydney Memory and Ageing Study (Sydney MAS) and the Older Australian Twins Study (OATS) (n = 942) revealed genome-wide significant results in or near the APOH gene on chromosome 17 (top SNP, rs7211380, p = 1 × 10⁻¹¹). The results were replicated in an independent cohort, the Hunter Community Study (p < 0.002) (n = 313). Conditional and joint analysis (COJO) confirmed the association of the chromosomal 17 region with ApoH levels. The set of independent SNPs identified by COJO explained 23% of the variance. The relationships between the top SNPs and cardiovascular/lipid/cognition measures and diabetes were assessed in Sydney MAS, with suggestive results observed for diabetes and cognitive performance. However, replication of these results in the smaller OATS cohort was not found. This work provides impetus for future research to better understand the contribution of genetics to ApoH levels and its possible impacts on health.

Genetic determinants of plasma β₂-glycoprotein I levels: a genome-wide association study in extended pedigrees from Spain

BACKGROUND

β2 -Glycoprotein I (β2 -GPI), also designated apolipoprotein H, is a 50-kDa protein that circulates in blood at high concentrations, playing important roles in autoimmune diseases, hemostasis, atherogenesis, and angiogenesis, as well as in host defense against bacteria and in protein/cellular waste removal. Plasma β2 -GPI levels have a significant genetic component (heritability of ~ 80%).

OBJECTIVES

To present the results of a genome-wide association study for plasma β2 -GPI levels in a set of extended pedigrees from the Genetic Analysis of Idiopathic Thrombophilia (GAIT) Project.

PATIENTS/METHODS

A total of 306 individuals for whom β2 -GPI plasma measurements were available were typed for 307,984 single-nucleotide polymorphisms (SNPs) with the Infinium 317k Beadchip (Illumina). Association with the β2 -GPI phenotype was investigated through variance component analysis, and the most significant results were followed up for association with coronary artery disease (CAD) in an independent in silico analysis involving 5765 CAD cases from the PROCARDIS Project and 7264 controls from the PROCARDIS Project and the Wellcome Trust Case Control Consortium (WTCCC) collection.

RESULTS

After correction for multiple testing, three SNPs located in/around two genes (ELF5 and SCUBE2) reached genome-wide significance. Moreover, an SNP in the APOH gene showed suggestive association with the β2 -GPI phenotype. Some of the identified genes are plausible biological candidates, as they are actually or potentially involved in inflammatory processes.

CONCLUSIONS

Our results represent a first step towards identifying common variants reflecting the genetic architecture influencing plasma β2 -GPI levels, and warrant further validation by functional experiments, as the functions of some of the discovered loci are still unknown.

Death is associated with complement C3 depletion in cerebrospinal fluid of patients with pneumococcal meningitis

Pneumococcal meningitis can lead to death or serious neurological sequelae as a result of the host inflammatory response. We investigated the association between host response protein expression and outcome in patients with pneumococcal meningitis. Cerebrospinal fluid (CSF) was obtained from 80 patients with pneumococcal meningitis (40 nonsurvivors and 40 survivors) and 10 normal controls. Candidate proteins were analyzed for an association with survival. Complement C3 levels were 5-fold lower in nonsurvivors than in survivors (P < 0.05). This C3 reduction was not associated with lower levels in serum, indicating a compartmentalized CSF response. Transferrin levels were significantly higher in CSF (but not serum) from nonsurvivors than in CSF from survivors, suggestive of blood-brain barrier damage. Classical apoptosis proteins caspase 3 and apoptosis-inducing factor were not present in CSF. Expression of creatine kinase BB in clinically infected CSF suggested neuronal necrosis, but there was no clear association between level of expression and clinical outcome. Increased blood-brain barrier permeability and complement C3 depletion may have a role in determining outcome from bacterial meningitis. Therapeutic use of citicoline or caspase inhibitors is unlikely to have beneficial effects in patients with meningitis.

We previously identified proteins associated with clinical outcome in patients diagnosed with pneumococcal meningitis in a pilot proteomics study of cerebrospinal fluid (CSF). In this article, we have quantitatively assayed specific proteins identified from this previous proteomics analysis along with proteins associated with cell death by using Western blotting.

Val247Leu β2-glycoprotein-I allelic variant is associated with antiphospholipid syndrome: systematic review and meta-analysis

INTRODUCTION

Previous studies have suggested that the possession of the Val/Val genotype of the Val247Leu polymorphism of the β(2)-glycoproteinI (β(2)-GPI) gene may be associated with antiphospholipid syndrome (APS), and, among patients with APS, with the production of anti-β(2)-GPI antibodies or the development of thrombosis. Given the controversial results reported, the aim of this work is to combine previous findings by means of a systematic review and a meta-analysis.

METHODS

We retrieved studies analyzing the genotype of the above-mentioned polymorphism among patients with APS by means of electronic database search. A meta-analysis was conducted in a random effects model and calculations of odds ratio (OR) and confidence intervals (CI) were done. Sensitivity analysis and tests for heterogeneity of the results were performed.

RESULTS

Eight previous studies analyzed the association of APS, anti-β(2)-GPI antibodies and/or thrombosis with the Val247Leu polymorphism. After meta-analysis, patients with APS had a significantly higher prevalence of the Val/Val genotype of this genetic variant when compared with controls (OR=2.04; 95% CI: 1.12, 3.73; P=0.02). Among patients with APS, those with anti-β(2)-GPI antibodies had a higher prevalence of this genotype (OR=1.73; 95% CI: 1.04, 2.87; P=0.03). No significant results were found for the presence of arterial or venous thrombosis.

CONCLUSIONS

Val/Val genotype of β(2)-GPI gene is associated with a significant excess risk to suffer from APS and, among patients with APS, to have anti-β(2)-GPI antibodies. No definite conclusions can be made regarding the association of this polymorphism with thrombosis among APS patients.

β2-glycoprotein I and protection from anti-SSA/Ro60-associated cardiac manifestations of neonatal lupus

One mechanism to molecularly explain the strong association of maternal anti-Ro60 Abs with cardiac disease in neonatal lupus (NL) is that these Abs initiate injury by binding to apoptotic cardiomyocytes in the fetal heart. Previous studies have demonstrated that β(2)-glycoprotein I (β(2)GPI) interacts with Ro60 on the surface of apoptotic Jurkat cells and prevents binding of anti-Ro60 IgG. Accordingly, the current study was initiated to test two complementary hypotheses, as follows: 1) competition between β(2)GPI and maternal anti-Ro60 Abs for binding apoptotic induced surface-translocated Ro60 occurs on human fetal cardiomyocytes; and 2) circulating levels of β(2)GPI influence injury in anti-Ro60-exposed fetuses. Initial flow cytometry experiments conducted on apoptotic human fetal cardiomyocytes demonstrated dose-dependent binding of β(2)GPI. In competitive inhibition experiments, β(2)GPI prevented opsonization of apoptotic cardiomyocytes by maternal anti-Ro60 IgG. ELISA was used to quantify β(2)GPI in umbilical cord blood from 97 neonates exposed to anti-Ro60 Abs, 53 with cardiac NL and 44 with no cardiac disease. β(2)GPI levels were significantly lower in neonates with cardiac NL. Plasmin-mediated cleavage of β(2)GPI prevented binding to Ro60 and promoted the formation of pathogenic anti-Ro60 IgG-apoptotic cardiomyocyte complexes. In aggregate these data suggest that intact β(2)GPI in the fetal circulation may be a novel cardioprotective factor in anti-Ro60-exposed pregnancies.

Proteomic analysis of cerebrospinal fluid in pneumococcal meningitis reveals potential biomarkers associated with survival

BACKGROUND

Patients with pneumococcal meningitis often die or have severe neurological damage despite optimal antibiotic therapy. New or improved therapy is required. The delivery of new interventions will require an improved understanding of the disease pathogenesis. Our objective was to learn more about the pathophysiology of severe meningitis through the interpretation of differences in the proteomic profile of cerebrospinal fluid (CSF) from patients with meningitis.

METHODS

Two-dimensional polyacrylamide gel electrophoresis of CSF from normal subjects (controls, n = 10) and patients with pneumococcal meningitis (n = 20) was analyzed. Spot differences were compared and identified between controls, nonsurvivors (n = 9), and survivors (n = 11).

RESULTS

Protein concentration in CSF of patients with meningitis was 4-fold higher than in CSF of control subjects (7.0 mg/mL vs 0.23 mg/mL; P < .01). A mean of 2466 discrete protein spots was present in CSF of patients with meningitis. Thirty-four protein spots were differentially expressed in CSF of nonsurvivors, compared with survivors. None of these protein spots were observed in CSF of control subjects.

CONCLUSIONS

Proteomic screening of CSF yields potential biomarkers capable of differentiating control subjects from nonsurvivors and survivors of meningitis. Proteins involved in the inflammatory process and central metabolism were represented in the differentially expressed protein repertoire.

Val/Leu247 polymorphism of beta2-glycoprotein I in Brazilian patients with antiphospholipid syndrome--a genetic risk factor?

A genetic polymorphism of the beta2-glycoprotein I (beta2-GPI) is recognized by antiphospholipid antibodies (aPL) and may even play a role in the development of antiphospholipid syndrome (APS). The objectives of this study were to determine a Val/Leu SNP at position 247 of the beta2-GPI gene in Brazilian patients with APS and to compare these data with clinical and laboratory manifestations. Polymorphism assignment was performed by PCR followed by Rsa I restriction endonuclease. The titration of anti-beta2-GPI antibodies was detected by ELISA. The results showed significantly higher frequencies of the V-encoding allele and the homozygous VV genotype in patients with APS than in control subjects (OR = 1.781, P = 0.0068; and OR = 6.413, P < 0.0001, respectively). The frequency of this genotype was also significantly higher in patients with arterial and venous thrombosis than in the control group (52% and 44%, respectively, versus 13%). Anti-beta2-GPI-positive patients had significantly higher frequencies of the VV genotype than the controls subjects (OR = 8.179, P < 0.0001). These results suggest that the V-encoding allele and the homozygous VV genotype at position 247 of the beta2-GPI gene may play a role in the generation of anomalous beta2-GPI, with consequent auto-antibody production, and in phenotype expression of arterial and venous thrombosis in APS patients.

Catastrophic antiphospholipid syndrome: treatment, prognosis, and the risk of relapse

The "catastrophic" variant of the antiphospholipid syndrome (APS) is characterized by multiple vascular occlusive events, usually affecting small vessels and developing over a short period of time. Although patients with catastrophic APS represent less than 1% of all patients with APS, they are usually in a life-threatening situation with a 50% mortality rate. The purpose of this paper is to review the treatment strategies and prognostic factors in patients with catastrophic APS. A detailed description of the clinical and laboratory features of the syndrome can be found in the other articles of this issue.

Ro 60 functions as a receptor for beta(2)-glycoprotein I on apoptotic cells

OBJECTIVE

The autoantigens 60-kd Ro/SSA (Ro 60) and beta(2)-glycoprotein I (beta(2)GPI) are both displayed on the surface membrane of apoptotic cells. Epitope-spreading experiments have suggested that these autoantigens may be present as a complex on the apoptotic cell surface. This study was undertaken to investigate whether beta(2)GPI interacts with Ro 60 on apoptotic cells and alters the binding of anti-Ro 60 IgG.

METHODS

The interaction between soluble recombinant Ro 60 fragments and beta(2)GPI was investigated in vitro by direct and saturation binding assays using native human beta(2)GPI and recombinant domain deletion mutants. Binding of beta(2)GPI to early and late apoptotic cells was assessed by multiparameter flow cytometry, and specificity of binding was determined by competitive inhibition with soluble recombinant Ro 60 and anti-Ro 60 IgG.

RESULTS

The Ro 60 fragment expressing a surface-exposed epitope (apotope) bound with high affinity (K(d) = approximately 15 nM) to domain V of beta(2)GPI in vitro. Beta(2)-glycoprotein I bound to the surface of apoptotic cells in a dose-dependent manner and was blocked by the Ro 60 apotope fragment. In reciprocal competitive inhibition studies, beta(2)GPI blocked the binding of anti-Ro 60 autoantibodies to apoptotic cells in a dose-dependent manner, and anti-Ro 60 IgG inhibited the binding of beta(2)GPI. Moreover, beta(2)GPI showed a 2-fold increase in binding to apoptotic cells that overexpress Ro 60 on the surface.

CONCLUSION

These results demonstrate that Ro 60 functions as a novel receptor for beta(2)GPI on the surface of apoptotic cells. The formation of Ro 60-beta(2)GPI complexes may protect against anti-Ro 60 autoantibody-mediated tissue injury.

Beta2-glycoprotein I and annexin A5 phospholipid interactions: artificial and cell membranes

The aim of this report was an overview of beta2-glycoprotein I (beta2-GPI)- and annexin A5 (AnxA5)-phospholipid interactions including candidate beta2-GPI receptors, and their relevance to the investigation of physiological/pathological processes. Both beta2-GPI and AnxA5 have thrombomodulatory functions in vivo and their antigenicity is particularly important for thrombotic manifestations and pregnancy complications in antiphospholipid syndrome. Specific elements of beta2-GPI- and AnxA5-phospholipid interactions are different. The crucial elements for beta2-GPI are conformational change and dimerization, both of which are also required and necessary for receptor signaling, leading to the prothombotic state. AnxA5 differs in its ability to crystallize into a protective shield, the disruption of which seems to be the major prothrombotic mechanism. These differences may explain some of the functional consequences of both molecules seen in the pathological conditions. Future alternative therapies of antiphospholipid syndrome are proposed to be based on the expanding knowledge of beta2-GPI- and AnxA5-phospholipid interactions, specifically antagonizing beta2-GPI receptors, as well as inhibiting their signaling pathways.

The physiopathology of the catastrophic antiphospholipid (Asherson's) syndrome: compelling evidence

Catastrophic antiphospholipid (Asherson's) syndrome (cAPS) was described in the past as a severe variant of the antiphospholipid syndrome (APS). Currently growing evidence suggests it is a unique condition. This statement is based on several clinical and physiopathological features that although not well understood define cAPS by itself. The remarkable features of cAPS are the presence of antiphospholipid antibodies (aPLAs) and microthromboses. Additional physiopathological features are the presence of anemia and thrombocytopenia, which are also often described in similar autoimmune conditions. A strong association with concomitant infection is thought to act as the main trigger of microthromboses in cAPS. Several theories have been proposed to explain these physiopathological features. Some of them suggest the possibility of molecular mimicry between components of infectious microorganisms and natural anticoagulants, which might be involved in the production of cross-reacting aPLAs in cAPS. Some genetic risk factors have also been suggested to be implicated in the onset of cAPS, however they have not been defined yet. Herein, we review the remarkable physiopathological features commonly described in cAPS hitherto. We concluded that although they are not completely understood, it is possible to differentiate them from similar conditions. Nevertheless further studies on these physiopathological mechanisms of the disease are needed.

Predictive, protective, orphan autoantibodies: the example of anti-phospholipid antibodies

Anti-phospholipid antibodies (aPL) are one of the most recent examples of autoantibodies that can appear even long time before any clinical manifestation can be associated with them. There is a general agreement that they may represent a strong risk factor for recurrent thrombosis and/or fetal losses. Anti-phospholipid antibodies represent a necessary but not sufficient factor (first hit) for thrombosis, and require additional triggering factors (second hit) to disclose the thrombogenic activity. Several factors may affect the predictive value of aPL, including titre, immunoglobulin isotype, fine antigenic specificity and affinity binding activity. Their careful evaluation is suggested in order to characterize the true predictive value of aPL.

Thrombolysis in antiphospholipid syndrome: current hematologic perspectives

Antiphospholipid antibodies (aPL) can cause thromboembolic events, but the reason for the thrombogenesis has not been fully elucidated. Studies show that the true pathogenic targets of aPL are plasma proteins involved in hemostasis (eg, beta(2)-glycoprotein I and prothrombin). These plasma proteins in turn bind to phospholipids, leading to the misclassification as "antiphospholipid" antibodies. The hemostatic system has abundant checks and balances to avoid excess hemorrhage and thrombosis. Thus, thrombosis requires more than interrupting one protein in the complex system. This review examines host genetic factors important in predisposition to thrombosis associated with aPL and concentrates on how antibodies in antiphospholipid syndrome interact with our natural anticoagulants and lead to thrombosis.