Antibodies against dengue virus nonstructural protein-1 induce heme oxygenase-1 via a redox-dependent pathway in human endothelial cells

Naringenin-induced HO-1 ameliorates high glucose or free fatty acids-associated apoptosis via PI3K and JNK/Nrf2 pathways in human umbilical vein endothelial cells

Naringenin (NG), a flavanone extracted from various plants, has potent vasoprotective effects likely related to the induction of heme oxygenase-1 (HO-1). In the current study, we investigated mechanisms underlying the effect of NG on HO-1 expression and high glucose (HG)- or free fatty acids (FFA)-induced apoptosis in human umbilical vein endothelial cells (HUVECs). First, we found that HUVECs exposed to NG exhibited enhanced HO-1 expression in a concentration- and time-dependent manner. Moreover, HUVECs treated with NG exhibited activation of phosphoinositide 3 kinase (PI3K)/Akt, extracellular-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK). LY294002 (a PI3K inhibitor) and SP600125 (a JNK inhibitor) reduced NG-induced HO-1 expression, whereas BIRB796 (a p38 inhibitor) and PD98059 (an ERK inhibitor) had no effect. The cytoprotective effects of NG were correlated with activation of the transcription factor NF-E2-related factor 2 (Nrf2), a critical regulator of HO-1 expression. Indeed, the results of our experiments using LY294002 and SP600125 indicated that NG may stimulate Nrf2 through PI3K/Akt and JNK pathway activation. Moreover, treatment of HUVECs with Nrf2 siRNA decreased NG-induced HO-1 expression. Finally, pretreatment of HUVECs with NG remarkably reduced HG- or FFA-induced cell apoptosis, and this effect was greatly abrogated in the presence of SnPP (an HO-1 inhibitor). Above all, our data show that NG increased HO-1 expression and reduced HG- or FFA-induced cell apoptosis in HUVECs by upregulating PI3K, JNK, and Nrf2 pathways, which may confer an adaptive survival response in diabetes-induced vascular injury.

HLA class II antibodies induce necrotic cell death in human endothelial cells via a lysosomal membrane permeabilization-mediated pathway

Antibody-mediated rejection (AMR) is the major cause of allograft loss after solid organ transplantation. Circulating donor-specific antibodies against human leukocyte antigen (HLA), in particular HLA class II antibodies are critical for the pathogenesis of AMR via interactions with endothelial cells (ECs). To investigate the effects of HLA class II antibody ligation to the graft endothelium, a model of HLA-DR antibody-dependent stimulation was utilized in primary human ECs. Antibody ligation of HLA class II molecules in interferon-γ-treated ECs caused necrotic cell death without complement via a pathway that was independent of apoptosis and necroptosis. HLA-DR-mediated cell death was blocked by specific neutralization of antibody ligation with recombinant HLA class II protein and by lentiviral knockdown of HLA-DR in ECs. Importantly, HLA class II-mediated cytotoxicity was also induced by relevant native allele-specific antibodies from human allosera. Necrosis of ECs in response to HLA-DR ligation was mediated via hyperactivation of lysosomes, lysosomal membrane permeabilization (LMP), and release of cathepsins. Notably, LMP was caused by reorganization of the actin cytoskeleton. This was indicated by the finding that LMP and actin stress fiber formation by HLA-DR antibodies were both downregulated by the actin polymerization inhibitor cytochalasin D and inhibition of Rho GTPases, respectively. Finally, HLA-DR-dependent actin stress fiber formation and LMP led to mitochondrial stress, which was revealed by decreased mitochondrial membrane potential and generation of reactive oxygen species in ECs. Taken together, ligation of HLA class II antibodies to ECs induces necrotic cell death independent of apoptosis and necroptosis via a LMP-mediated pathway. These findings may enable novel therapeutic approaches for the treatment of AMR in solid organ transplantation.

Plugging the Leak in Dengue Shock

Recent structural and functional advances provide fresh insight into the biology of the dengue virus non-structural protein, NS1 and suggest new avenues of research. The work of our lab and others have shown that the secreted, hexameric form of NS1 has a systemic toxic effect, inducing inflammatory cytokines and acting directly on endothelial cells to produce the hallmark of dengue disease, vascular leak. We also demonstrated that NS1 exerts its toxic activity through recognition by the innate immune receptor TLR4, mimicking the bacterial endotoxin LPS. This monograph covers the background underpinning these new findings and discusses new avenues for antiviral and vaccine intervention.

Heme Oxygenase-1 Inhibits HLA Class I Antibody-Dependent Endothelial Cell Activation

Antibody-mediated rejection (AMR) is a key limiting factor for long-term graft survival in solid organ transplantation. Human leukocyte antigen (HLA) class I (HLA I) antibodies (Abs) play a major role in the pathogenesis of AMR via their interactions with HLA molecules on vascular endothelial cells (ECs). The antioxidant enzyme heme oxygenase (HO)-1 has anti-inflammatory functions in the endothelium. As complement-independent effects of HLA I Abs can activate ECs, it was the goal of the current study to investigate the role of HO-1 on activation of human ECs by HLA I Abs. In cell cultures of various primary human macro- and microvascular ECs treatment with monoclonal pan- and allele-specific HLA I Abs up-regulated the expression of inducible proinflammatory adhesion molecules and chemokines (vascular cell adhesion molecule-1 [VCAM-1], intercellular cell adhesion molecule-1 [ICAM-1], interleukin-8 [IL-8] and monocyte chemotactic protein 1 [MCP-1]). Pharmacological induction of HO-1 with cobalt-protoporphyrin IX reduced, whereas inhibition of HO-1 with either zinc-protoporphyrin IX or siRNA-mediated knockdown increased HLA I Ab-dependent up-regulation of VCAM-1. Treatment with two carbon monoxide (CO)-releasing molecules, which liberate the gaseous HO product CO, blocked HLA I Ab-dependent EC activation. Finally, in an in vitro adhesion assay exposure of ECs to HLA I Abs led to increased monocyte binding, which was counteracted by up-regulation of HO-1. In conclusion, HLA I Ab-dependent EC activation is modulated by endothelial HO-1 and targeted induction of this enzyme may be a novel therapeutic approach for the treatment of AMR in solid organ transplantation.

Novel anti-thrombotic agent for modulation of protein disulfide isomerase family member ERp57 for prophylactic therapy

Protein disulfide isomerase (PDI) family members including PDI and ERp57 emerge as novel targets for anti-thrombotic treatments, but chemical agents with selectivity remain to be explored. We previously reported a novel derivative of danshensu (DSS), known as ADTM, displayed strong cardioprotective effects against oxidative stress-induced cellular injury in vitro and acute myocardial infarct in vivo. Herein, using chemical proteomics approach, we identified ERp57 as a major target of ADTM. ADTM displayed potent inhibitory effects on the redox activity of ERp57, inhibited the adenosine diphosphate (ADP)-induced expressions of P-selectin and αIIbβ3 integrin, and disrupted the interaction between ERp57 and αIIbβ3. In addition, ADTM inhibited both arachidonic acid (AA)-induced and ADP-induced platelet aggregation in vitro. Furthermore, ADTM significantly inhibited rat platelet aggregation and thrombus formation in vivo. Taken together, ADTM represents a promising candidate for anti-thrombotic therapy targeting ERp57.

Correlation between serum levels of anti-endothelial cell autoantigen and anti-dengue virus nonstructural protein 1 antibodies in dengue patients

We have previously shown that anti-dengue virus nonstructural protein 1 (anti-DENV NS1) antibodies cross-react with endothelial cells, and several autoantigens have been identified. This study shows that the antibody levels against these self-proteins are higher in sera from patients with dengue hemorrhagic fever (DHF) than those in control sera. Anti-protein disulfide isomerase (PDI) and anti-heat shock protein 60 (anti-HSP60) IgM levels correlated with both anti-endothelial cells and anti-DENV NS1 IgM titers. A cross-reactive epitope on the NS1 amino acid residues 311-330 (P311-330) had been predicted. We further found that there were higher IgM and IgG levels against P311-330 in DHF patients' sera than those in the control sera. In addition, correlations were observed between anti-PDI with anti-P311-330 IgM and IgG levels, respectively. Therefore, our results indicate that DENV NS1 P311-330 is a major epitope for cross-reactive antibodies to PDI on the endothelial cell surface, which may play an important role in DENV infection-induced autoimmunity.

Protein disulfide isomerase mediates dengue virus entry in association with lipid rafts

Dengue virus (DENV) causes a febrile disease, infecting around 50-100 million people annually. The relationship between DENV proteins and host cellular responses during infection is unclear. This study investigated the interaction of host protein disulfide isomerase (PDI) with DENV proteins and role of lipid rafts in viral immunopathogenesis. Host viral protein interactions were studied by co-immunoprecipitation and co-localization. It was found that PDI interacts with DENV nonstructural protein 1 (NS1) intracellularly as well as on the surface in the lipid raft domain. Disruption of this key interaction between PDI and NS1 could be an important therapeutic strategy to block DENV infection.

Endothelial dysfunction in dengue virus pathology

Dengue virus (DENV) is a leading cause of illness and death, mainly in the (sub)tropics, where it causes dengue fever and/or the more serious diseases dengue hemorrhagic fever and dengue shock syndrome that are associated with changes in vascular permeability. Despite extensive research, the pathogenesis of DENV is still poorly understood and, although endothelial cells represent the primary fluid barrier of the blood vessels, the extent to which these cells contribute to DENV pathology is still under debate. The primary target cells for DENV are dendritic cells and monocytes/macrophages that release various chemokines and cytokines upon infection, which can activate the endothelium and are thought to play a major role in DENV-induced vascular permeability. However, recent studies indicate that DENV also replicates in endothelial cells and that DENV-infected endothelial cells may directly contribute to viremia, immune activation, vascular permeability and immune targeting of the endothelium. Also, the viral non-structural protein-1 and antibodies directed against this secreted protein have been reported to be involved in endothelial cell dysfunction. This review provides an extensive overview of the effects of DENV infection on endothelial cell physiology and barrier function.

A highly conserved region between amino acids 221 and 266 of dengue virus non-structural protein 1 is a major epitope region in infected patients

The immune response to dengue virus (DENV) infection generates high levels of antibodies (Abs) against the DENV non-structural protein 1 (NS1), particularly in cases of secondary infection. Therefore, anti-NS1 Abs may play a role in severe dengue infections, possibly by interacting (directly or indirectly) with host factors or regulating virus production. If it does play a role, NS1 may contain epitopes that mimic those epitopes of host molecules. Previous attempts to map immunogenic regions within DENV-NS1 were undertaken using mouse monoclonal Abs (MAbs). The aim of this study was to characterize the epitope regions of nine anti-NS1 human monoclonal Abs (HuMAbs) derived from six patients secondarily infected with DENV-2. These anti-NS1 HuMAbs were cross-reactive with DENV-1, -2, and -3 but not DENV-4. All HuMAbs bound a common epitope region located between amino acids 221 and 266 of NS1. This study is the first report to map a DENV-NS1 epitope region using anti-DENV MAbs derived from patients.

Anti-human neutrophil antigen-3a induced transfusion-related acute lung injury in mice by direct disturbance of lung endothelial cells

OBJECTIVE

Antibodies against human neutrophil antigen-3a (HNA-3a) located on choline transporter-like protein 2 induce severe transfusion-related acute lung injury (TRALI). This study aims to identify the mechanism implicated in anti-HNA-3a-mediated TRALI.

APPROACH AND RESULTS

Our analysis shows that anti-HNA-3a recognizes 2 choline transporter-like protein 2 isoforms (P1 and P2) on human microvascular endothelial cells from lung blood vessels but reacts only with the P1 isoform on neutrophils. Direct treatment of HNA-3a-positive endothelial cells with anti-HNA-3a, but not with anti-HNA-3b, leads to reactive oxygen species production, increased albumin influx, and decreased endothelial resistance associated with the formation of actin stress filaments and loosening of junctional vascular endothelium-cadherin. In a novel in vivo mouse model, TRALI was documented by significant increase in lung water content, albumin concentration, and neutrophil numbers in the bronchoalveolar lavage on injection of human anti-HNA-3a in lipopolysaccharides-treated, as well as nontreated mice. Interestingly, although neutrophil depletion alleviated severity of lung injury, it failed to prevent TRALI in this model. Infusion of anti-HNA-3a F(ab')2 fragments caused moderate TRALI. Finally, mice lacking nicotinamide adenine dinucleotide phosphate oxidase (NOX2(y/-)) were protected from anti-HNA-3a-mediated TRALI.

CONCLUSIONS

These data demonstrate the initiation of endothelial barrier dysfunction in vitro and in vivo by direct binding of anti-HNA-3a on endothelial cells. It seems, however, that the presence of neutrophils aggravates barrier dysfunction. This novel mechanism of TRALI primarily mediated by endothelial cell dysfunction via choline transporter-like protein 2 may help to define new treatment strategies to decrease TRALI-related mortality.

The flavivirus NS1 protein: molecular and structural biology, immunology, role in pathogenesis and application as a diagnostic biomarker

The flavivirus nonstructural glycoprotein NS1 is an enigmatic protein whose structure and mechanistic function have remained somewhat elusive ever since it was first reported in 1970 as a viral antigen circulating in the sera of dengue-infected patients. All flavivirus NS1 genes share a high degree of homology, encoding a 352-amino-acid polypeptide that has a molecular weight of 46-55 kDa, depending on its glycosylation status. NS1 exists in multiple oligomeric forms and is found in different cellular locations: a cell membrane-bound form in association with virus-induced intracellular vesicular compartments, on the cell surface and as a soluble secreted hexameric lipoparticle. Intracellular NS1 co-localizes with dsRNA and other components of the viral replication complex and plays an essential cofactor role in replication. Although this makes NS1 an ideal target for inhibitor design, the precise nature of its cofactor function has yet to be elucidated. A plethora of potential interacting partners have been identified, particularly for the secreted form of NS1, with many being implicated in immune evasion strategies. Secreted and cell-surface-associated NS1 are highly immunogenic and both the proteins themselves and the antibodies they elicit have been implicated in the seemingly contradictory roles of protection and pathogenesis in the infected host. Finally, NS1 is also an important biomarker for early diagnosis of disease. In this article, we provide an overview of these somewhat disparate areas of research, drawing together the wealth of data generated over more than 40 years of study of this fascinating protein.