A Possible Solution to the Paradox of the “Lupus Anticoagulant”: Antiphospholipid Antibodies Accelerate Thrombin Generation by Inhibiting Annexin-V

Proteomics analysis of differentially expressed proteins in chicken trachea and kidney after infection with the highly virulent and attenuated coronavirus infectious bronchitis virus in vivo

BACKGROUND

Infectious bronchitis virus (IBV) is first to be discovered coronavirus which is probably endemic in all regions with intensive impact on poultry production. In this study, we used two-dimensional gel electrophoresis (2-DE) and two-dimensional fluorescence difference gel electrophoresis (2-DIGE), coupled with matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF/TOF-MS), to explore the global proteome profiles of trachea and kidney tissues from chicken at different stages infected in vivo with the highly virulent ck/CH/LDL/97I P5 strain of infectious bronchitis virus (IBV) and the embryo-passaged, attenuated ck/CH/LDL/97I P115 strain.

RESULTS

Fifty-eight differentially expressed proteins were identified. Results demonstrated that some proteins which had functions in cytoskeleton organization, anti-oxidative stress, and stress response, showed different change patterns in abundance from chicken infected with the highly virulent ck/CH/LDL/97I P5 strain and those given the embryo-passaged, attenuated P115 stain. In addition, the dynamic transcriptional alterations of 12 selected proteins were analyzed by the real-time RT-PCR, and western blot analysis confirmed the change in abundance of heat shock proteins (HSP) beta-1, annexin A2, and annexin A5.

CONCLUSIONS

The proteomic alterations described here may suggest that these changes to protein expression correlate with IBV virus' virulence in chicken, hence provides valuable insights into the interactions of IBV with its host and may also assist with investigations of the pathogenesis of IBV and other coronavirus infections.

Annexin A2 in amniotic fluid: correlation with histological chorioamnionitis, preterm premature rupture of membranes, and subsequent preterm delivery

AIM

The aim of this study was to determine whether amniotic fluid levels of annexin A2, a phospholipid-binding protein that is abundant in amnion and regulates fibrin homeostasis, are associated with histological chorioamnionitis, preterm premature rupture of the membranes, and subsequent preterm delivery.

MATERIALS AND METHODS

Amniotic fluid was obtained from 55 pregnant women with preterm labor and/or preterm premature rupture of the membranes before 32weeks of gestation, and amniotic fluid levels of annexin A2 were measured with a sandwich enzyme-linked immunosorbent assay.

RESULTS

Amniotic fluid levels of annexin A2 in patients with histological chorioamnionitis was higher than that in the remainder (P=0.053), whereas amniotic fluid levels of annexin A2 in patients with preterm premature rupture of the membranes was significantly higher than that in the remainder (P=0.002). Amniotic levels of annexin A2 was a fair test (area under receiver-operator characteristic curve=0.679), and amniotic fluid levels of annexin A2>878.2ng/mL had a sensitivity of 68.8%, a specificity of 65.2%, a positive predictive value of 73.3%, and a negative predictive value of 60.0% for predicting delivery within 2weeks after amniotic fluid sampling. Furthermore, the combined use of amniotic fluid cut-off levels of 878.2ng/mL for annexin A2 and 13.3ng/mL for interleukin-8 improved the specificity (91.3%) and the positive predictive value (89.5%).

CONCLUSIONS

We identified amniotic fluid levels of annexin A2, especially in combination with amniotic fluid levels of interleukin-8, as a novel predictive marker for preterm delivery.

Antiphospholipid antibodies: paradigm in transition

OBJECTIVES

This is a critical review of anti-phospholipid antibodies (aPL). Most prior reviews focus on the aPL syndrome (APS), a thrombotic condition often marked by neurological disturbance. We bring to attention recent evidence that aPL may be equally relevant to non-thrombotic autoimmune conditions, notably, multiple sclerosis and ITP.

ORGANIZATION

After a brief history, the recent proliferation of aPL target antigens is reviewed. The implication is that many more exist. Theories of aPL in thrombosis are then reviewed, concluding that all have merit but that aPL may have more diverse pathological consequences than now recognized. Next, conflicting results are explained by methodological differences. The lupus anticoagulant (LA) is then discussed. LA is the best predictor of thrombosis, but why this is true is not settled. Finally, aPL in non-thrombotic disorders is reviewed.

CONCLUSION

The current paradigm of aPL holds that they are important in thrombosis, but they may have much wider clinical significance, possibly of special interest in neurology.

Hydroxychloroquine directly reduces the binding of antiphospholipid antibody-beta2-glycoprotein I complexes to phospholipid bilayers

Treatment with the antimalarial drug hydroxychloroquine (HCQ) has been associated with reduced risk of thrombosis in the antiphospholipid (aPL) syndrome (APS) and, in an animal model of APS, with reduction of experimentally induced thrombosis. Recognition of beta2-glycoprotein I (beta2GPI) by aPL antibodies appears to play a major role in the disease process. We therefore used the techniques of ellipsometry and atomic force microscopy (AFM) to investigate whether HCQ directly affects the formation of aPL IgG-beta2GPI complexes on phospholipid bilayers. HCQ, at concentrations of 1 mug/mL and greater, significantly reduced the binding of aPL-beta2GPI complexes to phospholipid surfaces and THP-1 (human acute monocytic leukemia cell line) monocytes. The drug also reduced the binding of the individual proteins to bilayers. This HCQ-mediated reduction of binding was completely reversed when the HCQ-protein solutions were dialyzed against buffer. HCQ also caused modest, but statistically significant, reductions of clinical antiphospholipid assays. In conclusion, HCQ reduces the formation of aPL-beta2GPI complexes to phospholipid bilayers and cells. This effect appears to be due to reversible interactions between HCQ and the proteins and may contribute to the observed reduction of thrombosis in human and experimental APS. These results support the possibility that HCQ, or analogous molecules, may offer novel nonanticoagulant therapeutic strategies for treating APS.

Annexins and disease

The annexins are a family of closely related calcium- and membrane-binding proteins expressed in most eukaryotic cell types. Despite their structural and biochemical similarities annexins have diverse functions, in cellular activities that include vesicle trafficking, cell division, apoptosis, calcium signalling, and growth regulation. To date there is no evidence to suggest that any individual member of the annexin family is a disease-causing gene, i.e., a gene that through loss, mutation, translocation or amplification leads to a known human disease. However, there is good evidence that in certain clinical conditions, changes in annexin expression levels or localisation may contribute to the pathological consequences and sequelae of disease. In this way, annexins are indirectly linked to some of the most serious human disease classes including cardiovascular disease and cancer. In this review we consider the roles played by annexins in disease and examine the molecular basis for anomalous annexin behaviour that may contribute to disease pathophysiology.

Human monoclonal antiphospholipid antibodies disrupt the annexin A5 anticoagulant crystal shield on phospholipid bilayers: evidence from atomic force microscopy and functional assay

The antiphospholipid (aPL) syndrome is an autoimmune condition that is marked by recurrent pregnancy losses and/or systemic vascular thrombosis in patients who have antibodies against phospholipid/co-factor complexes. The mechanism(s) for pregnancy losses and thrombosis in this condition is (are) not known. Annexin A5 is a potent anticoagulant protein, expressed by placental trophoblasts and endothelial cells, that crystallizes over anionic phospholipids, shielding them from availability for coagulation reactions. We previously presented data supporting the hypothesis that aPL antibody-mediated disruption of the anticoagulant annexin A5 shield could be a thrombogenic mechanism in the aPL syndrome. However, this has remained a subject of controversy. We therefore used atomic force microscopy, a method previously used to study the crystallization of annexin A5, to image the effects of monoclonal human aPL antibodies on the crystal structure of the protein over phospholipid bilayers. In the presence of the aPL monoclonal antibodies (mAbs) and beta(2)-GPI, the major aPL co-factor, structures presumed to be aPL mAb-antigen complexes were associated with varying degrees of disruption to the annexin A5 crystallization pattern over the bilayer. In addition, measurements of prothrombinase activity on the phospholipid bilayers showed that the aPL mAbs reduced the anti-coagulant effect of annexin A5 and promoted thrombin generation. These data provide morphological evidence that support the hypothesis that aPL antibodies can disrupt annexin A5 binding to phospholipid membranes and permit increased generation of thrombin. The aPL antibody-mediated disruption of the annexin A5 anticoagulant shield may be an important prothrombotic mechanism in the aPL syndrome.

The antiphospholipid syndrome

The antiphospholipid (aPL) antibody syndrome is an autoimmune condition in which vascular thrombosis and/or recurrent pregnancy losses occur in patients with laboratory evidence for antibodies that bind to phospholipids. There have been significant advances in the recognition of the role of phospholipid-binding cofactors, primarily beta2GPI, as the true immunologic targets of the antibodies. Recent evidence suggests that the antibodies disrupt phospholipid-dependent anticoagulant mechanisms and/or that aPL antibodies induce the expression of procoagulant and proadhesive molecules on endothelial cells. Current diagnosis is based on clinical findings and empirically derived tests, such as assays for antibodies that bind to phospholipids or putative cofactors and coagulation assays that detect inhibition of phospholipid-dependent coagulation reactions. Current treatment relies primarily on anticoagulant therapy. Research advances are expected to bring mechanistically based diagnostic tests and improved therapy that target the roots of the disease process.

Antiphospholipid antibodies: discovery, definitions, detection and disease

Antiphospholipid antibodies (aPL) are immunoglobulins of IgG, IgM and IgA isotypes that target phospholipid (PL) and/or PL-binding plasma proteins. Detection of aPL in the laboratory is done currently by both immunoassays and functional coagulation tests. Convention defines aPL specificity in immunoassays according to the particular PL substrate present, for example aPS represents antiphosphatidylserine antibodies. This may be technically incorrect inasmuch as a particular PL may be responsible for binding and highly concentrating a specific plasma protein, the latter then becomes the target for the aPL. The binding of beta(2)GP-I (apolipoprotein H) to the negatively charged PL, cardiolipin (CL) provides a good example of this circumstance. In contrast, aPL which specifically prolong coagulation times in in vitro are called lupus anticoagulants (LA). The precise PL target(s) of the aPL responsible for LA activities are unknown and often debated. The persistent finding of aPL in patients in association with abnormal blood clotting and a myriad of neurological, obstetrical and rheumatic disorders often compounded by autoimmune diseases has led to an established clinical diagnosis termed antiphospholipid syndrome (APS). The common denominator for these APS patients is the presence of circulating aPL on two or more occasions and the observation of events attributable to abnormal or accelerated blood clotting somewhere in vivo. The purpose of this review is to collect, collate, and consolidate information concerning aPL.

Molecular pathogenesis of the antiphospholipid syndrome

The antiphospholipid (aPL) syndrome is an acquired autoimmune disorder of unknown etiology in which patients present with thrombosis together with laboratory evidence for antibodies in blood that recognize anionic phospholipid-protein complexes. The main antigenic target for the aPL antibodies has been identified to be beta(2) glycoprotein I (beta(2)GPI), a phospholipid-binding protein. The high affinity of aPL antibody-beta(2)GPI complex for phospholipid membranes seems to be a critical step in the mechanism of this disease. This review focuses on some of the major mechanisms that have been proposed to explain this disorder.

Transient visual symptoms in systemic lupus erythematosus and antiphospholipid syndrome

PURPOSE

To review the potential pathogenic mechanisms of transient visual symptoms (TVS) in the course of systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS), to discuss the most common clinical features associated with the occurrence of TVS, and to explore possible treatment options for these patients.

METHODS

The literature regarding the clinical and laboratory characteristics of SLE and APS patients experiencing TVS is reviewed from 1979 onward. A brief review of the wide spectrum of ophthalmologic features occurring in SLE and APS is also provided.

RESULTS

Data emerging from the review process point to thromboembolism as the most probable cause of TVS in SLE and APS. Thromboembolisms are likely induced by cardiac valve abnormalities and should be treated with anticoagulant drugs.

CONCLUSION

While progress has been made in understanding the association of TVS with SLE and APS, further investigation is needed to clarify this interesting relationship.

The annexinopathies: a new category of diseases

The annexins are a family of highly homologous phospholipid binding proteins, which share a four-domain structure, with one member of the family - annexin VI - having a duplication consisting of eight domains. Thus far, ten annexins have been described in mammals. Although the biological functions of the annexins have not been definitively established, two human diseases involving annexin abnormalities ('annexinopathies') have been identified as of the time of writing. Overexpression of annexin II occurs in the leukocytes of a subset of patients having a hemorrhagic form of acute promyelocytic leukemia. Underexpression of annexin V occurs on placental trophoblasts in the antiphospholipid syndrome and in preeclampsia. Also, an animal model has been described in which annexin VII is underexpressed and is associated with disease, but the relevance of this animal model to human disease is not yet understood. Future research is likely to elucidate additional 'annexinopathies'.

Antiphospholipid antibody-mediated disruption of the annexin-V antithrombotic shield: a thrombogenic mechanism for the antiphospholipid syndrome

The mechanism(s) for thrombosis and pregnancy losses in the anti-phospholipid antibody syndrome have not yet been established. Annexin-V is an anionic phospholipid-binding protein with potent anticoagulant activity. The protein has been shown to be necessary for the maintenance of placental integrity and may play a thromboregulatory role at the maternal-fetal interface. There, it assembles over the apical surfaces of the placental villi and shields the underlying anionic phospholipids from availability for complexation with coagulation proteins. We have proposed that thrombosis and pregnancy loss in the antiphospholipid syndrome may be due to the disruption of the annexin-V shield by antiphospholipid (and co-factor) antibodies. The data accumulated from tissue immunohistochemistry, trophoblast and endothelial cell culture studies, coagulation studies using non-cellular phospholipids, and competition studies on artificial phospholipid bilayer are consistent with this hypothesis.

The pathogenic role of annexin-V in the antiphospholipid syndrome

The antiphospholipid antibody syndrome is an autoimmune condition in which venous or arterial thrombosis and recurrent pregnancy losses occur in patients having serologic evidence of antibodies against anionic phospholipid-protein complexes. The pathophysiologic mechanisms of this syndrome have not yet been established. Annexin-V, an anionic phospholipid-binding protein with potent anticoagulant activity, is necessary for maintenance of placental integrity and may play a thromboregulatory role at the vascular-blood interface by forming two-dimensional crystals which shield anionic phospholipids from complexing with coagulation proteins from circulating blood. We propose that thrombosis and pregnancy loss in the antiphospholipid syndrome may be caused by disruption of this Annexin-V shield by antiphospholipid (and cofactor) antibodies, thereby increasing the net quantity of thrombogenic phospholipids exposed to the circulating blood. The data accumulated from tissue immunohistochemistry, trophoblast and endothelial cell culture studies, coagulation studies using noncellular phospholipids, and competition studies on artificial phospholipid bilayer are consistent with the hypothesis that interference with the binding of Annexin-V to anionic phospholipid surfaces is an important mechanism of thrombosis and pregnancy loss in the antiphospholipid syndrome.