Complement Activation and Thrombin Generation by MBL Bound to ß2-Glycoprotein I.

ß2-Glycoprotein I (ß2-GPI) is an abundant plasma glycoprotein with unknown physiological function and is currently recognized as the main target of antiphospholipid Abs responsible for complement activation and vascular thrombosis in patients with antiphospholipid syndrome (APS). In this study, we provide evidence that mannose-binding lectin (MBL) binds to ß2-GPI in Ca++ and a dose-dependent manner and that this interaction activates complement and promotes complement-dependent thrombin generation. Surprisingly, a significant binding was observed between MBL and isolated domains II and IV of ß2-GPI, whereas the carbohydrate chains, domain I and domain V, were not involved in the interaction, documenting a noncanonical binding mode between MBL and ß2-GPI. Importantly, this interaction may occur on endothelial cells because binding of MBL to ß2-GPI was detected on the surface of HUVECs, and colocalization of MBL with ß2-GPI was observed on the endothelium of a biopsy specimen of a femoral artery from an APS patient. Because ß2-GPI-mediated MBL-dependent thrombin generation was increased after priming the endothelium with TNF-α, our data suggests that this mechanism could play an important yet unrecognized role under physiological conditions and may be upregulated in pathological situations. Moreover, the complement activation and the procoagulant effects of the ß2-GPI/MBL complex may contribute to amplify similar activities of anti-ß2-GPI Abs in APS and possibly act independently of Abs, raising the issue of developing appropriate therapies to avoid recurrences and disability in patients at risk for these clinical conditions.

ß2 Glycoprotein I Recognition Drives Th1 Inflammation in Atherosclerotic Plaques of Patients with Primary Antiphospholipid Syndrome.

Antiphospholipid syndrome (APS) is characterized by recurrent arterial/venous thrombosis and miscarriages in the persistent presence of autoantibodies against phospholipid-binding proteins (aPLs), such as ß2 glycoprotein I (ß2GPI). In addition to the aPL thrombophilic effect, arterial thrombosis was related to accelerated atherosclerosis in animal models; however, contrasting findings were reported in primary APS patients with regard to the increased number of plaques or abnormal arterial wall thickness. We investigated the cytokine production induced by ß2GPI in activated T cells that infiltrate in vivo atherosclerotic lesions of primary APS patients with atherothrombosis. We also examined the helper function of ß2GPI-specific T cells for monocyte matrix metalloproteinase-9 and tissue factor production, as well as their cytolytic potential and their helper function for Ab production. APS patients with atherothrombosis harbor in vivo-activated CD4+ T cells that recognize ß2GPI in atherothrombotic lesions. ß2GPI induces T cell proliferation and IFN-γ expression in plaque-derived T cell clones. ß2GPI-specific T cells display helper function for monocyte matrix metalloproteinase-9 and tissue factor production and promote Ig production in autologous B cells. Moreover, plaque-derived ß2GPI-specific CD4+ T lymphocytes express perforin-mediated and Fas/Fas ligand-mediated cytotoxicity. ß2GPI, and especially the DI domain, drive a local Th1 inflammatory response, with subsequent plaque instability that eventually favors atherothrombosis. This finding may explain the association between aPLs and arterial thrombosis, despite the lack of evidence of surrogate markers for atherosclerosis in primary APS.

A non-complement-fixing antibody to ß2 glycoprotein I as a novel therapy for antiphospholipid syndrome.

A single-chain fragment variable (scFv) recognizing ß2-glycoprotein 1 (ß2GPI) from humans and other species was isolated from a human phage display library and engineered to contain an IgG1 hinge-CH2-CH3 domain. The scFv-Fc directed against ß2GPI domain I-induced thrombosis and fetal loss, thus mimicking the effect of antibodies from patients with antiphospholipid syndrome (APS). Complement is involved in the biological effect of anti-ß2GPI scFv-Fc, as demonstrated by its ability to promote in vitro and in vivo complement deposition and the failure to induce vascular thrombosis in C6-deficient rats and fetal loss in C5-depleted mice. A critical role for complement was also supported by the inability of the CH2-deleted scFv-Fc to cause vessel occlusion and pregnancy failure. This antibody prevented the pathological effects of anti-ß2GPI antibodies from APS patients and displaced ß2GPI-bound patient antibodies. The CH2-deleted antibody represents an innovative approach potentially useful to treat APS patients refractory to standard therapy.

Antiphospholipid Antibodies and Infertility: A Gene Expression Study in Decidual Stromal Cells.

BACKGROUND: Antiphospholipid antibodies (aPL) have been advocated as potential mediators of unexplained female infertility, but no evidence has yet been raised to support such an association. OBJECTIVES: To test the hypothesis that aPL might interfere with uterine decidualization, a gene expression study was performed on decidual stromal cells treated with different aPL preparations. METHODS: Decidual stromal cells were isolated from first-trimester deciduas obtained from two women undergoing elective abortion, and treated with: (i) a ß2GPI-dependent aPL monoclonal antibody (IS3); (ii) IS3 plus TIFI, a synthetic peptide mimicking PL-binding region of ß2GPI; and (iii) IgG from healthy subjects (NHS). Gene expression data were acquired using human HT-12 v3 beadchip arrays (Illumina). Differential expression analysis was performed by fitting a gene-wise linear model using the treatment group and decidual source as covariates. RESULTS: In the comparison of IS3 versus IgG NHS-treated decidual cells, gene ontology (GO) enrichment was expressed in terms relating to well-characterized aPL-mediated cellular effects: "inflammatory response," "immune response," "response to stress," "oxydoreductase activity," "metalloendopeptidase activity," and "cytokine/chemokine activity." As expected, almost all genes were up-regulated by IS3 treatment. The same GO categories appeared to be differentially expressed when IS3 treatment was compared to IS3 + TIFI, but with most genes being down-regulated. CONCLUSIONS: Given the inflammatory response evinced on gene expression analysis of decidual stromal cells treated with a ß2GPI -dependent aPL monoclonal antibody, it is feasible that aPL might interfere with uterine decidualization, affecting the early stages of implantation and ultimately resulting in female infertility.

Interferon and B-cell Signatures Inform Precision Medicine in Lupus Nephritis.

Introduction: Current therapeutic management of lupus nephritis (LN) fails to induce long-term remission in over 50% of patients, highlighting the urgent need for additional options. Methods: We analyzed differentially expressed genes (DEGs) in peripheral blood from patients with active LN (n = 41) and active nonrenal lupus (n = 62) versus healthy controls (HCs) (n = 497) from the European PRECISESADS project (NTC02890121), and dysregulated gene modules in a discovery (n = 26) and a replication (n = 15) set of active LN cases. Results: Replicated gene modules qualified for correlation analyses with serologic markers, and regulatory network and druggability analysis. Unsupervised coexpression network analysis revealed 20 dysregulated gene modules and stratified the active LN population into 3 distinct subgroups. These subgroups were characterized by low, intermediate, and high interferon (IFN) signatures, with differential dysregulation of the "B cell" and "plasma cells/Ig" modules. Drugs annotated to the IFN network included CC-motif chemokine receptor 1 (CCR1) inhibitors, programmed death-ligand 1 (PD-L1) inhibitors, and irinotecan; whereas the anti-CD38 daratumumab and proteasome inhibitor bortezomib showed potential for counteracting the "plasma cells/Ig" signature. In silico analysis demonstrated the low-IFN subgroup to benefit from calcineurin inhibition and the intermediate-IFN subgroup from B-cell targeted therapies. High-IFN patients exhibited greater anticipated response to anifrolumab whereas daratumumab appeared beneficial to the intermediate-IFN and high-IFN subgroups. Conclusion: IFN upregulation and B and plasma cell gene dysregulation patterns revealed 3 subgroups of LN, which may not necessarily represent distinct disease phenotypes but rather phases of the inflammatory processes during a renal flare, providing a conceptual framework for precision medicine in LN.

In vivo distribution of ß2 glycoprotein I under various pathophysiologic conditions.

In vitro studies have documented ß2 glycoprotein I (ß2GPI) binding to endothelial cells (ECs) and trophoblast using antiphospholipid antibodies. The in vivo binding of ß2GPI to these cells and the conditions that favor their interaction have not been investigated. We analyzed the in vivo distribution of cyanine 5.5-labeled ß2GPI in mice and evaluated the effect of pregnancy and circulating antibodies on its tissue localization. The signal was detected in the liver by whole body scan and ex vivo analysis. The ß2GPI failed to bind to the vascular endothelium and reacted only with the ECs of uterine vessels. In pregnant mice the protein was localized on ECs and trophoblast at the embryo implantation sites. Immunized mice showed a similar ß2GPI biodistribution to naive mice but the immunized pregnant animals exhibited a significant increase in fetal loss associated with C3 and C9 deposition at the implantation sites. Treatment of mice with LPS after ß2GPI-Cy5.5 injection promoted protein localization on gut and brain ECs associated with IgG, C1q, and C9 deposition in immunized mice. These findings indicate that ß2GPI binding to EC requires priming with pro-inflammatory factors which is not needed for uterine and placental localization probably dependent on hormonal changes.

Updating on the pathogenic mechanisms 5 of the antiphospholipid antibodies-associated pregnancy loss.

Anti-phospholipid antibodies (aPL) are risk factor for recurrent pregnancy loss and obstetrical complications. The mechanisms of aPL-mediated pregnancy failure are still a matter of research. Although aPL are associated with thrombosis, thrombotic events cannot explain all the miscarriages. There is evidence for a direct in vitro aPL effect on the trophoblast as shown by their binding; reduction of proliferation, human chorionic gonadotrophin release, in vitro invasiveness, adhesion molecule expression; and increased apoptosis. Such a direct reactivity is supported by the expression of beta2 glycoprotein (beta 2GP) I on trophoblast cell membranes. aPL/anti-beta 2GPI antibodies also bind to human decidual/endometrial cells in vitro and induce a pro-inflammatory phenotype. APL-mediated inflammatory processes at the placental level are apparently responsible for fetal loss at least in animal models. Both complement activation and pro-inflammatory cytokine/chemokine secretion have been shown to play a role. More recently, complement-induced tissue factor expression on infiltrating neutrophils was described as an additional pathogenic mechanisms mediated by aPL. As a whole, these findings do suggest that aPL may induce a defective placentation by acting at different levels without involving necessarily thrombotic events.

Synergistic activity of everolimus and 5-aza-2'-deoxycytidine in medullary thyroid carcinoma cell lines.

Medullary thyroid cancer (MTC) is a tumor highly resistant to chemo- and radiotherapy. Drug resistance can be induced by epigenetic changes such as aberrant DNA methylation. To overcome drug resistance, we explored a promising approach based on the use of 5-aza-2'-deoxycytidine (AZA), a demethylating agent, in combination with the mTOR inhibitor everolimus in MTC cells (MZ-CRC-1 and TT). This combined treatment showed a strong synergistic antiproliferative activity through the induction of apoptosis. The effect of everolimus and/or AZA on genome-wide expression profiling was evaluated by Illumina BeadChip in MZ-CRC-1 cells. An innovative bioinformatic pipeline identified four potential molecular pathways implicated in the synergy between AZA and everolimus: PI3K-Akt signaling, the neurotrophin pathway, ECM/receptor interaction, and focal adhesion. Among these, the neurotrophin signaling pathway was most directly involved in apoptosis, through the overexpression of NGFR and Bax genes. The increased expression of genes involved in the NGFR-MAPK10-TP53-Bax/Bcl2 pathway during incubation with AZA plus everolimus was validated by western blotting in MZ-CRC-1 cells. Interestingly, addition of a neutralizing anti-NGFR antibody inhibited the synergistic cytotoxic activity between AZA and everolimus. These results open a new therapeutic scenario for MTC and potentially other neuroendocrine tumors, where therapy with mTOR inhibitors is currently approved.

Humoral autoimmunity against endothelium: theory or reality?

Despite the discovery of anti-endothelial cell antibodies (AECA) in a heterogeneous group of disorders characterized by endothelial damage, their pathogenic role is still debated. Experimental in vitro models indicate that they can either damage endothelial cells or trigger cell signaling by reacting with as yet undefined surface molecules. However, clinical studies suggest that, in addition to AECA, other pathogenic mechanisms are involved in the vasculitic process. Recently, antibodies specific for beta2 glycoprotein I, the phospholipid-binding protein targeted by anti-phospholipid antibodies, have been shown to display anti-endothelial activity. These autoantibodies recognize beta2 glycoprotein I adhered to the endothelium and induce a cell perturbation that might underlie the thrombophilic state of the anti-phospholipid syndrome.

Role of the MyD88 transduction signaling pathway in endothelial activation by antiphospholipid antibodies.

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by the persistent presence of antiphospholipid antibodies (aPLs) and recurrent thrombosis or fetal loss. The thrombophilic state has been partially related to the induction of a proinflammatory and procoagulant endothelial cell (EC) phenotype induced by anti-beta(2)-glycoprotein I (beta(2)-GPI) antibodies that bind beta(2)-GPI expressed on the EC surface. Anti-beta(2)-GPI antibody binding has been shown to induce nuclear factor-kappa B (NF-kappa B) translocation leading to a proinflammatory EC phenotype similar to that elicited by interaction with microbial products (lipopolysaccharide [LPS]) and proinflammatory cytokines (interleukin 1 beta [IL-1 beta], tumor necrosis factor alpha [TNF-alpha]). However, the upstream signaling events are not characterized yet. To investigate the endothelial signaling cascade activated by anti-beta(2)-GPI antibodies, we transiently cotransfected immortalized human microvascular endothelial cells (HMEC-1) with dominant-negative constructs of different components of the pathway (Delta TRAF2, Delta TRAF6, Delta MyD88) together with reporter genes (NF-kappa B luciferase and pCMV-beta-galactosidase). Results showed that both human anti-beta(2)-GPI IgM monoclonal antibodies as well as polyclonal affinity-purified anti-beta(2)-GPI IgG display a signaling cascade comparable to that activated by LPS or IL-1. Delta TRAF6 and Delta MyD88 significantly abrogate antibody-induced as well as IL-1- or LPS-induced NF-kappa B activation, whereas Delta TRAF2 (involved in NF-kappa B activation by TNF) does not affect it. Moreover, anti- beta(2)-GPI antibodies and LPS followed the same time kinetic of IL-1 receptor-activated kinase (IRAK) phosphorylation, suggesting an involvement of the toll-like receptor (TLR) family. Our findings demonstrate that anti-beta(2)-GPI antibodies react with their antigen likely associated to a member of the TLR/IL-1 receptor family on the EC surface and directly induce activation.