XAF1 contributes to dengue virus-induced apoptosis in vascular endothelial cells

Mechanisms of programmed cell death associated to severe dengue in human renal lesions

Dengue virus (DENV) is a global health problem. Severe dengue can manifest with hemorrhage and signs of organ dysfunction, including the kidneys. The innate immune system is an important barrier against arbovirus infection and, specifically in dengue, the cytokines IL1β and IL18 and caspase-1 activation make up a set of host immune strategies. Cell death mechanisms include pyroptosis, necroptosis and autophagy, each with peculiar markers: gasdermin, RIPK3/MLKL, LC3, respectively. In DENV infection, necrosis and apoptosis are involved and, when infecting monocytes and macrophages in vitro, DENV is capable of inducing pyroptosis. Our objective was to explore the presence of markers of necroptosis, pyroptosis and autophagy in renal lesions caused by DENV.

MATERIAL AND METHODS

twenty specimens of lesions from patients who died due to DENV infection, from the pathology department of Hospital Guilherme Álvaro, Santos, SP, were subjected to histological and immunohistochemical studies. Histological sections were stained with hematoxylin-eosin to evaluate tissue changes or collected for research with antibodies: anti-DENV (Instituto Evandro Chagas-PA), RIPK3 (NBP2-45592), MLKL (ab184718), gasdermin D (#36425 ), LC3 (14600-AP), caspase 1 (#98033), IL1β (AF201-NA) and IL18 (SC6178). Semi-quantitative analysis was performed on 20 glomeruli and evaluation on tubules and mononuclear cells. This study was approved by the ethics committee of the USP Faculty of Medicine.

RESULTS

histological analysis demonstrated glomerular congestion, glomerulitis (medium to severe), acute kidney injury and hyalinization of the glomeruli. Viral antigens were visualized on mononuclear cells. LC3 (autophagy) expression ranged from moderate to intense (++/+++) in glomeruli, tubules and mononuclear cells. The expression of gasdermin (pyroptosis) was mild (+) in most cases in the glomeruli and moderate (++) in the tubules. RIPK3 and MLKL (necroptosis) mild in tubules and mononuclear cells (+). The expression of the cytokines IL1β and IL18 and caspase 1 was moderate (++). Statistical analysis showed greater expression of LC3 over the others.

CONCLUSIONS

Our results contribute to the understanding of the pathogenesis of renal involvement in severe dengue, considering the likely anti-viral mechanism of autophagy. To a lesser extent, pyroptosis is also present, corroborating previous data.

XAF1 Protects Host against Emerging RNA Viruses by Stabilizing IRF1-Dependent Antiviral Immunity

XIAP-associated factor 1 (XAF1) is an interferon (IFN)-stimulated gene (ISG) that enhances IFN-induced apoptosis. However, it is unexplored whether XAF1 is essential for the host fighting against invaded viruses. Here, we find that XAF1 is significantly upregulated in the host cells infected with emerging RNA viruses, including influenza, Zika virus (ZIKV), and SARS-CoV-2. IFN regulatory factor 1 (IRF1), a key transcription factor in immune cells, determines the induction of XAF1 during antiviral immunity. Ectopic expression of XAF1 protects host cells against various RNA viruses independent of apoptosis. Knockout of XAF1 attenuates host antiviral innate immunity in vitro and in vivo, which leads to more severe lung injuries and higher mortality in the influenza infection mouse model. XAF1 stabilizes IRF1 protein by antagonizing the CHIP-mediated degradation of IRF1, thus inducing more antiviral IRF1 target genes, including DDX58, DDX60, MX1, and OAS2. Our study has described a protective role of XAF1 in the host antiviral innate immunity against RNA viruses. We have also elucidated the molecular mechanism that IRF1 and XAF1 form a positive feedback loop to induce rapid and robust antiviral immunity. IMPORTANCE Rapid and robust induction of antiviral genes is essential for the host to clear the invaded viruses. In addition to the IRF3/7-IFN-I-STAT1 signaling axis, the XAF1-IRF1 positive feedback loop synergistically or independently drives the transcription of antiviral genes. Moreover, XAF1 is a sensitive and reliable gene that positively correlates with the viral infection, suggesting that XAF1 is a potential diagnostic marker for viral infectious diseases. In addition to the antitumor role, our study has shown that XAF1 is essential for antiviral immunity. XAF1 is not only a proapoptotic ISG, but it also stabilizes the master transcription factor IRF1 to induce antiviral genes. IRF1 directly binds to the IRF-Es of its target gene promoters and drives their transcriptions, which suggests a unique role of the XAF1-IRF1 loop in antiviral innate immunity, particularly in the host defect of IFN-I signaling such as invertebrates.

Flaviviruses: Innate Immunity, Inflammasome Activation, Inflammatory Cell Death, and Cytokines

The innate immune system is the host’s first line of defense against the invasion of pathogens including flavivirus. The programmed cell death controlled by genes plays an irreplaceable role in resisting pathogen invasion and preventing pathogen infection. However, the inflammatory cell death, which can trigger the overflow of a large number of pro-inflammatory cytokines and cell contents, will initiate a severe inflammatory response. In this review, we summarized the current understanding of the innate immune response, inflammatory cell death pathway and cytokine secretion regulation during Dengue virus, West Nile virus, Zika virus, Japanese encephalitis virus and other flavivirus infections. We also discussed the impact of these flavivirus and viral proteins on these biological processes. This not only provides a scientific basis for elucidating the pathogenesis of flavivirus, but also lays the foundation for the development of effective antiviral therapies.

Apoptosis during ZIKA Virus Infection: Too Soon or Too Late?

Cell death by apoptosis is a major cellular response in the control of tissue homeostasis and as a defense mechanism in the case of cellular aggression such as an infection. Cell self-destruction is part of antiviral responses, aimed at limiting the spread of a virus. Although it may contribute to the deleterious effects in infectious pathology, apoptosis remains a key mechanism for viral clearance and the resolution of infection. The control mechanisms of cell death processes by viruses have been extensively studied. Apoptosis can be triggered by different viral determinants through different pathways as a result of virally induced cell stresses and innate immune responses. Zika virus (ZIKV) induces Zika disease in humans, which has caused severe neurological forms, birth defects, and microcephaly in newborns during the last epidemics. ZIKV also surprised by revealing an ability to persist in the genital tract and in semen, thus being sexually transmitted. Mechanisms of diverting antiviral responses such as the interferon response, the role of cytopathic effects and apoptosis in the etiology of the disease have been widely studied and debated. In this review, we examined the interplay between ZIKV infection of different cell types and apoptosis and how the virus deals with this cellular response. We illustrate a duality in the effects of ZIKV-controlled apoptosis, depending on whether it occurs too early or too late, respectively, in neuropathogenesis, or in long-term viral persistence. We further discuss a prospective role for apoptosis in ZIKV-related therapies, and the use of ZIKV as an oncolytic agent.

Potential Molecular Mechanisms and Remdesivir Treatment for Acute Respiratory Syndrome Corona Virus 2 Infection/COVID 19 Through RNA Sequencing and Bioinformatics Analysis

Introduction:

Severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) infections (COVID 19) is a progressive viral infection that has been investigated extensively. However, genetic features and molecular pathogenesis underlying remdesivir treatment for SARS-CoV-2 infection remain unclear. Here, we used bioinformatics to investigate the candidate genes associated in the molecular pathogenesis of remdesivir-treated SARS-CoV-2-infected patients.

Methods:

Expression profiling by high-throughput sequencing dataset (GSE149273) was downloaded from the Gene Expression Omnibus, and the differentially expressed genes (DEGs) in remdesivir-treated SARS-CoV-2 infection samples and nontreated SARS-CoV-2 infection samples with an adjusted P value of <.05 and a |log fold change| > 1.3 were first identified by limma in R software package. Next, pathway and gene ontology (GO) enrichment analysis of these DEGs was performed. Then, the hub genes were identified by the NetworkAnalyzer plugin and the other bioinformatics approaches including protein-protein interaction network analysis, module analysis, target gene—miRNA regulatory network, and target gene—TF regulatory network. Finally, a receiver-operating characteristic analysis was performed for diagnostic values associated with hub genes.

Results:

A total of 909 DEGs were identified, including 453 upregulated genes and 457 downregulated genes. As for the pathway and GO enrichment analysis, the upregulated genes were mainly linked with influenza A and defense response, whereas downregulated genes were mainly linked with drug metabolism—cytochrome P450 and reproductive process. In addition, 10 hub genes (VCAM1, IKBKE, STAT1, IL7R, ISG15, E2F1, ZBTB16, TFAP4, ATP6V1B1, and APBB1) were identified. Receiver-operating characteristic analysis showed that hub genes (CIITA, HSPA6, MYD88, SOCS3, TNFRSF10A, ADH1A, CACNA2D2, DUSP9, FMO5, and PDE1A) had good diagnostic values.

Conclusion:

This study provided insights into the molecular mechanism of remdesivir-treated SARS-CoV-2 infection that might be useful in further investigations.

Targets and strategies for vaccine development against dengue viruses

Dengue virus (DENV) is a global health threat causing about half of the worldwide population to be at risk of infection, especially the people living in tropical and subtropical area. Although the dengue disease caused by dengue virus (DENV) is asymptomatic and self-limiting in most people with first infection, increased severe dengue symptoms may be observed in people with heterotypic secondary DENV infection. Since there is a lack of specific antiviral medication, the development of dengue vaccines is critical in the prevention and control this disease. Several targets and strategies in the development of dengue vaccine have been demonstrated. Currently, Dengvaxia, a live-attenuated chimeric yellow-fever/tetravalent dengue vaccine (CYD-TDV) developed by Sanofi Pasteur, has been licensed and approved for clinical use in some countries. However, this vaccine has demonstrated low efficacy in children and dengue-naïve individuals and also increases the risk of severe dengue in young vaccinated recipients. Accordingly, many novel strategies for the dengue vaccine are under investigation and development. Here, we conducted a systemic literature review according to PRISMA guidelines to give a concise overview of various aspects of the vaccine development process against DENVs, mainly targeting five potential strategies including live attenuated vaccine, inactivated virus vaccine, recombinant subunit vaccine, viral-vector vaccine, and DNA vaccine. This study offers the comprehensive view of updated information and current progression of immunogen selection as well as strategies of vaccine development against DENVs.

Dengue Virus Infection: A Tale of Viral Exploitations and Host Responses

Dengue is a mosquito-borne viral disease (arboviral) caused by the Dengue virus. It is one of the prominent public health problems in tropical and subtropical regions with no effective vaccines. Every year around 400 million people get infected by the Dengue virus, with a mortality rate of about 20% among the patients with severe dengue. The Dengue virus belongs to the Flaviviridae family, and it is an enveloped virus with positive-sense single-stranded RNA as the genetic material. Studies of the infection cycle of this virus revealed potential host targets important for the virus replication cycle. Here in this review article, we will be discussing different stages of the Dengue virus infection cycle inside mammalian host cells and how host proteins are exploited by the virus in the course of infection as well as how the host counteracts the virus by eliciting different antiviral responses.

Transcription Factor-Binding Site Identification and Enrichment Analysis

Transcription factors orchestrate complex regulatory networks of gene expression. A better understanding of the common transcription factors, and their shared interactions, among a set of coregulated or differentially expressed genes can provide powerful insights into the key pathways governing such expression patterns. Critically, such information must also be considered in the context of the frequency in which a transcription factor is present in a properly selected background, and in the context of existing evidence of gene and transcription factor interaction. Given the vast amount of publicly available gene expression data that can be further scrutinized by the user-friendly analysis tools described here, many useful insights are assuredly to be revealed. The proceeding methods for application of the analysis tool CiiiDER for transcription factor-binding site identification, enrichment analysis, and coregulatory factor identification should be applicable to any dataset comparing differential gene expression in response to various stimuli and gene coexpression datasets. These methods should assist the researcher in identifying the most relevant regulators within a gene set, and refining the list of targets for future study to those which may share biologically important regulatory networks.

The Dual Regulation of Apoptosis by Flavivirus

Apoptosis is a form of programmed cell death, which maintains cellular homeostasis by eliminating pathogen-infected cells. It contains three signaling pathways: death receptor pathway, mitochondria-mediated pathway, and endoplasmic reticulum pathway. Its importance in host defenses is highlighted by the observation that many viruses evade, hinder or destroy apoptosis, thereby weakening the host’s immune response. Flaviviruses such as Dengue virus, Japanese encephalitis virus, and West Nile virus utilize various strategies to activate or inhibit cell apoptosis. This article reviews the research progress of apoptosis mechanism during flaviviruses infection, including flaviviruses proteins and subgenomic flaviviral RNA to regulate apoptosis by interacting with host proteins, as well as various signaling pathways involved in flaviviruses-induced apoptosis, which provides a scientific basis for understanding the pathogenesis of flaviviruses and helps in developing an effective antiviral therapy.

Exposure to Dengue Envelope Protein Domain III Induces Nlrp3 Inflammasome-Dependent Endothelial Dysfunction and Hemorrhage in Mice

Typically occurring during secondary dengue virus (DENV) infections, dengue hemorrhagic fever (DHF) causes abnormal immune responses, as well as endothelial vascular dysfunction, for which the responsible viral factor remains unclear. During peak viremia, the plasma levels of virion-associated envelope protein domain III (EIII) increases to a point at which cell death is sufficiently induced in megakaryocytes in vitro. Thus, EIII may constitute a virulence factor for endothelial damage. In this study, we examined endothelial cell death induced by treatment with DENV and EIII in vitro. Notably, pyroptosis, the major type of endothelial cell death observed, was attenuated through treatment with Nlrp3 inflammasome inhibitors. EIII injection effectively induced endothelial abnormalities, and sequential injection of EIII and DENV-NS1 autoantibodies induced further vascular damage, liver dysfunction, thrombocytopenia, and hemorrhage, which are typical manifestations in DHF. Under the same treatments, pathophysiological changes in the Nlrp3 inflammasome–deficient mice were notably reduced compared with those in the wild-type mice. These results suggest that the Nlrp3 inflammasome constitutes a potential therapeutic target for treating DENV-induced hemorrhage in DHF.

Bioinformatics analyses of significant genes, related pathways, and candidate diagnostic biomarkers and molecular targets in SARS-CoV-2/COVID-19

Severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) infection is a leading cause of pneumonia and death. The aim of this investigation is to identify the key genes in SARS-CoV-2 infection and uncover their potential functions. We downloaded the expression profiling by high throughput sequencing of GSE152075 from the Gene Expression Omnibus database. Normalization of the data from primary SARS-CoV-2 infected samples and negative control samples in the database was conducted using R software. Then, joint analysis of the data was performed. Pathway and Gene ontology (GO) enrichment analyses were performed, and the protein-protein interaction (PPI) network, target gene - miRNA regulatory network, target gene - TF regulatory network of the differentially expressed genes (DEGs) were constructed using Cytoscape software. Identification of diagnostic biomarkers was conducted using receiver operating characteristic (ROC) curve analysis. 994 DEGs (496 up regulated and 498 down regulated genes) were identified. Pathway and GO enrichment analysis showed up and down regulated genes mainly enriched in the NOD-like receptor signaling pathway, Ribosome, response to external biotic stimulus and viral transcription in SARS-CoV-2 infection. Down and up regulated genes were selected to establish the PPI network, modules, target gene - miRNA regulatory network, target gene - TF regulatory network revealed that these genes were involved in adaptive immune system, fluid shear stress and atherosclerosis, influenza A and protein processing in endoplasmic reticulum. In total, ten genes (CBL, ISG15, NEDD4, PML, REL, CTNNB1, ERBB2, JUN, RPS8 and STUB1) were identified as good diagnostic biomarkers. In conclusion, the identified DEGs, hub genes and target genes contribute to the understanding of the molecular mechanisms underlying the advancement of SARS-CoV-2 infection and they may be used as diagnostic and molecular targets for the treatment of patients with SARS-CoV-2 infection in the future.

ERG-Associated lncRNA (ERGAL) Promotes the Stability and Integrity of Vascular Endothelial Barrier During Dengue Viral Infection via Interaction With miR-183-5p

Dengue virus (DENV) continues to be a major public health problem. DENV infection will cause mild dengue and severe dengue. Severe dengue is clinically manifested as serious complications, including dengue hemorrhagic fever and/or dengue shock syndrome (DHF/DSS), which is mainly characterized by vascular leakage. Currently, the pathogenesis of severe dengue is not elucidated thoroughly, and there are no known therapeutic targets for controlling the disease effectively. This study aimed to further reveal the potential molecular mechanism of severe dengue. In this study, the long non-coding RNA, ERG-associated lncRNA (lncRNA-ERGAL), was activated and significantly up-regulated in DENV-infected vascular endothelial cells. After knockdown of lncRNA-ERGAL, the expression of ERG, VE-cadherin, and claudin-5 was repressed; besides, cell apoptosis was enhanced, and cytoskeletal remodeling was disordered, leading to instability and increased permeability of vascular endothelial barrier during DENV infection. Fluorescence in situ hybridization (FISH) assay showed lncRNA-ERGAL to be mainly expressed in the cytoplasm. Moreover, the expression of miR-183-5p was found to increase during DENV infection and revealed to regulate ERG, junction-associated proteins, and the cytoskeletal structure after overexpression and knockdown. Then, ERGAL was confirmed to interact with miR-183-5p by luciferase reporter assay. Collectively, ERGAL acted as a miRNA sponge that can promote stability and integrity of vascular endothelial barrier during DENV infection via binding to miR-183-5p, thus revealing the potential molecular mechanism of severe dengue and providing a foundation for a promising clinical target in the future.

Mechanisms of monocyte cell death triggered by dengue virus infection

Arthropod-borne viral diseases caused by dengue virus (DENV) are major re-emerging public health problem worldwide. In spite of intense research, DENV pathogenesis is not fully understood and remains enigmatic; however, current evidence suggests that dengue progression is associated with an inflammatory response, mainly in patients suffering from a second DENV infection. Monocytes are one of the main target cells of DENV infection and play an important role in pathogenesis since they are known to produce several inflammatory cytokines that can lead to endothelial dysfunction and therefore vascular leak. In addition, monocytes play an important role in antibody dependent enhancement, infection with consequences in viral load and immune response. Despite the physiological functions of monocytes in immune response, their life span in the bloodstream is very short, and activation of monocytes by DENV infection can trigger different types of cell death. For example, DENV can induce apoptosis in monocytes related with the production of Tumor necrosis factor alpha (TNF-α). Additionally, recent studies have shown that DENV-infected monocytes also exhibit a cell death process mediated by caspase-1 activation together with IL-1 production, referred to as pyroptosis. Taken together, the aforementioned studies strongly depict that multiple cell death pathways may be occurring in monocytes upon DENV-2 infection. This review provides insight into mechanisms of DENV-induced death of both monocytes and other cell types for a better understanding of this process. Further knowledge in cell death induced by DENV will help in the developing novel strategies to prevent disease progression.

Zika Virus Transmission Through Blood Tissue Barriers

The recent Zika virus (ZIKV) epidemic in the Americas and the Caribbean revealed a new deadly strain of the mosquito-borne virus, which has never been associated with previous outbreaks in Asia. For the first time, widespread ZIKV infection was shown to cause microcephaly and death of newborns, which was most likely due to the mutation acquired during the large outbreak recorded in French Polynesia in 2013–2014. Productive ZIKV replication and persistence has been demonstrated in placenta and fetal brains. Possible association between ZIKV and microcephaly and fetal death has been confirmed using immunocompetent mouse models in vitro and in vivo. Having crossed the placenta, ZIKV directly targets neural progenitor cells (NPCs) in developing human fetus and triggers apoptosis. The embryonic endothelial cells are exceptionally susceptible to ZIKV infection, which causes cell death and tissue necrosis. On the contrary, ZIKV infection does not affect the adult brain microvascular cell morphology and blood–brain barrier function. ZIKV is transmitted primarily by Aedes mosquito bite and is introduced into the placenta/blood through replication at the site of the entry. Also, virus can be transmitted through unprotected sex. Although, multiple possible routes of virus infection have been identified, the exact mechanism(s) utilized by ZIKV to cross the placenta still remain largely unknown. In this review, the current understanding of ZIKV infection and transmission through the placental and brain barriers is summarized.

Dengue virus non-structural protein 1: a pathogenic factor, therapeutic target, and vaccine candidate

Dengue virus (DENV) infection is the most common mosquito-transmitted viral infection. DENV infection can cause mild dengue fever or severe dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS). Hemorrhage and vascular leakage are two characteristic symptoms of DHF/DSS. However, due to the limited understanding of dengue pathogenesis, no satisfactory therapies to treat nor vaccine to prevent dengue infection are available, and the mortality of DHF/DSS is still high. DENV nonstructural protein 1 (NS1), which can be secreted in patients’ sera, has been used as an early diagnostic marker for dengue infection for many years. However, the roles of NS1 in dengue-induced vascular leakage were described only recently. In this article, the pathogenic roles of DENV NS1 in hemorrhage and vascular leakage are reviewed, and the possibility of using NS1 as a therapeutic target and vaccine candidate is discussed.

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.

High dengue virus load differentially modulates human microvascular endothelial barrier function during early infection

Plasma leakage is the main pathophysiological feature in severe dengue, resulting from altered vascular barrier function associated with an inappropriate immune response triggered upon infection. The present study investigated functional changes using an electric cell-substrate impedance sensing system in four (brain, dermal, pulmonary and retinal) human microvascular endothelial cell (MEC) lines infected with purified dengue virus, followed by assessment of cytokine profiles and the expression of inter-endothelial junctional proteins. Modelling of changes in electrical impedance suggests that vascular leakage in dengue-infected MECs is mostly due to the modulation of cell-to-cell interactions, while this loss of vascular barrier function observed in the infected MECs varied between cell lines and DENV serotypes. High levels of inflammatory cytokines (IL-6 and TNF-α), chemokines (CXCL1, CXCL5, CXCL11, CX3CL1, CCL2 and CCL20) and adhesion molecules (VCAM-1) were differentially produced in the four infected MECs. Further, the tight junctional protein, ZO-1, was down-regulated in both the DENV-1-infected brain and pulmonary MECs, while claudin-1, PECAM-1 and VE-cadherin were differentially expressed in these two MECs after infection. Non-purified virus stock was also studied to investigate the impact of virus stock purity on dengue-specific immune responses, and the results suggest that virus stock propagated through cell culture may include factors that mask or alter the DENV-specific immune responses of the MECs. The findings of the present study show that high DENV load differentially modulates human microvascular endothelial barrier function and disrupts the function of inter-endothelial junctional proteins during early infection with organ-specific cytokine production.

Dengue virus induces apoptosis in SH-SY5Y human neuroblastoma cells

INTRODUCTION

Dengue is a human disease caused by a virus with the same name, which is transmitted by the bite of Aedes mosquitoes. The infection has a wide range of clinical presentations ranging from asymptomatic to fatal cases, with the pediatric population being the most susceptible. According to the new classification of the disease, the neurological manifestations are considered a criterion for the diagnosis of severe dengue. 

OBJECTIVE

To evaluate the possible mechanisms involved in the onset of neurological signs in a cell line of human neurons as a model of infection with dengue virus type 2 (DENV-2). 

MATERIALS AND METHODS

Susceptibility and permissiveness of the SH-SY5Y line to infection by DENV-2 was analyzed, showing that the proportions of viral infection and production are similar to those of primate cells used as positive control for infection. 

RESULTS

Infection induced a cytopathic effect on the neuroblastoma line characterized by apoptotic cell death process, increasing the proportion of annexin V and TUNEL positive cells and an upregulation of TNF-α. Treatment with anti-TNF-α antibody increased slightly cell survival of infected cells. The addition of exogenous TNF-α to the infected cultures enhanced cell death. 

CONCLUSION

These results as a whole suggest that the upregulation of TNF-α could be part of the process that induces cell damage and death in cases of dengue encephalitis.

IFI6 Inhibits Apoptosis via Mitochondrial-Dependent Pathway in Dengue Virus 2 Infected Vascular Endothelial Cells

Dengue hemorrhagic fever (DHF)/Dengue shock syndrome (DSS) is a fatal infectious disease that demands an effective treatment. Interferon (IFN)-stimulated genes (ISGs) induced by dengue virus (DENV) exert antiviral effects. Among ISGs, IFN-α inducible gene 6 (IFI6) was increased in DENV infected human umbilical vascular endothelial cells (HUVECs) by microarray analysis in our previous study. However, its function is incompletely understood. In this study, we confirmed that IFI6 was markedly induced in DENV infection of both primary HUVECs and EA.hy926 cell lines. Recombinant EA.hy926 cell lines in which IFI6 was either over-expressed (IFI6+/+) or knocked-down (IFI6-/-) were generated. The activation of caspase-3 and intrinsic apoptosis-related protein caspase-9 were down-regulated in IFI6+/+ but up-regulated in IFI6-/- cells at 24–48 hrs post-infection. After incubation with DENV for 48 hrs, the mitochondrial membrane potential (Δψ(m)) was more stable in IFI6+/+ cells but reduced in IFI6-/- cells, as assayed by fluorescence staining with JC-1. We observed that Bcl-2 expression was increased in IFI6+/+ and decreased in IFI6-/- cells. By contrast, Bax expression was decreased in IFI6+/+ and increased in IFI6-/- cells. It is presumed that the anti-apoptotic function of IFI6 is expressed by regulating the rheostatic balance between bcl-2/bax expression and inhibition of Δψ(m) depolarization during DENV infection of vascular endothelial cells(VECs). In addition, the pro-apoptotic protein X-linked Inhibitor of Apoptosis (XIAP)-Associated Factor 1(XAF1) expression had been reported to be up-regulated and led to the induction of apoptosis in DENV2-infected VECs,but the relationship between XAF1 and IFI6 dengue virus-induced apoptosis in VECs warrants further study.

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.

X-linked inhibitor of apoptosis-associated factor l (XAFl) enhances the sensitivity of colorectal cancer cells to cisplatin

The purpose of present study was to investigate the roles of X-linked inhibitor of apoptosis-associated factor l (XAFl) in regulation apoptosis of colorectal cancer (CRC) cells after treatment with cisplatin (DDP). A total of ten paired cancerous and non-cancerous tissues were collected from patients with CRC after surgery. The levels of XAFl protein were detected by Western blot. Primary CRC cells were separated from cancer tissues, and its viability or apoptosis after treatment with DDP was determined with MTT or Annexin V/PI assays, respectively. Furthermore, we either up-regulated transfecting a XAF1 overexpression vector or down-regulated XAF1 by siRNA interference. And then, the XAF1 levels and its sensitivity to cisplatin were assessed. XAFl had a lower expression in the cancerous tissues from samples T1, T2 and T3 than their paired non-cancerous tissues N1, N2 and N3. However, the expression of XAF1 was not detected in samples T4 and N1. XAF1 levels in cancer tissues significantly decreased in comparison with normal tissues. Cell abilities of primary cells were significantly decreased in a dose-dependent manner, after treatment with a series concentrations of cisplatin (2, 5, 10 μg/mL) for 48 h. Although, after down-expression of XAFl by siRNA, cisplatin caused a significant decreases in apoptosis rates in CRC cells. The up-regulation of XAF1 distinctly increased apoptosis in CRC cells administered by cisplatin (P < 0.001). The XAFl could promoted apoptosis and enhanced chemotherapy sensitivity to cisplatin in CRC cells.

Coordinated regulation of autophagy and apoptosis determines endothelial cell fate during Dengue virus type 2 infection

Dengue is the most prevalent mosquito-borne viral disease in tropical regions. Severe cases may progress to Dengue hemorrhagic fever, suggesting vascular endothelial dysfunction in disease pathogenesis. In our previous study, we found that Dengue virus type 2 (DENV2) induced apoptosis of vascular endothelial cells via FasL/Fas- and XIAP-associated factor 1 (XAF1)-dependent pathways. In this paper, we demonstrate that DENV2 can induce autophagy in primary human umbilical vein endothelial cells (HUVECs) and the human umbilical vein endothelial cell line EA.hy926. Inhibition of autophagy with 3-methyl adenine promoted apoptosis, while inhibition of apoptosis with Z-VAD-FMK facilitated autophagy in DENV2-infected HUVECs and EA.hy926 cells. Interferon-alpha-inducible protein 6 (IFI6), a putative apoptosis regulator, inhibited DENV2-induced autophagy in EA.hy926 cells, while XAF1, an inhibitor of anti-apoptotic XIAP, facilitated autophagy. Molecular regulators of apoptosis and autophagy interact at multiple levels to determine cell fate. Our data suggest that XAF1 and IFI6 are involved in regulating the balance between autophagy and apoptosis in DENV2-infected endothelial cells.

Regulation of cell survival and death during Flavivirus infections

Flaviviruses, ss(+) RNA viruses, include many of mankind’s most important pathogens. Their pathogenicity derives from their ability to infect many types of cells including neurons, to replicate, and eventually to kill the cells. Flaviviruses can activate tumor necrosis factor α and both intrinsic (Bax-mediated) and extrinsic pathways to apoptosis. Thus they can use many approaches for activating these pathways. Infection can lead to necrosis if viral load is extremely high or to other types of cell death if routes to apoptosis are blocked. Dengue and Japanese Encephalitis Virus can also activate autophagy. In this case the autophagy temporarily spares the infected cell, allowing a longer period of reproduction for the virus, and the autophagy further protects the cell against other stresses such as those caused by reactive oxygen species. Several of the viral proteins have been shown to induce apoptosis or autophagy on their own, independent of the presence of other viral proteins. Given the versatility of these viruses to adapt to and manipulate the metabolism, and thus to control the survival of, the infected cells, we need to understand much better how the specific viral proteins affect the pathways to apoptosis and autophagy. Only in this manner will we be able to minimize the pathology that they cause.

The pathology of severe dengue in multiple organs of human fatal cases: histopathology, ultrastructure and virus replication

Dengue is a public health problem, with several gaps in understanding its pathogenesis. Studies based on human fatal cases are extremely important and may clarify some of these gaps. In this work, we analyzed lesions in different organs of four dengue fatal cases, occurred in Brazil. Tissues were prepared for visualization in optical and electron microscopy, with damages quantification. As expected, we observed in all studied organ lesions characteristic of severe dengue, such as hemorrhage and edema, although other injuries were also detected. Cases presented necrotic areas in the liver and diffuse macro and microsteatosis, which were more accentuated in case 1, who also had obesity. The lung was the most affected organ, with hyaline membrane formation associated with mononuclear infiltrates in patients with pre-existing diseases such as diabetes and obesity (cases 1 and 2, respectively). These cases had also extensive acute tubular necrosis in the kidney. Infection induced destruction of cardiac fibers in most cases, with absence of nucleus and loss of striations, suggesting myocarditis. Spleens revealed significant destruction of the germinal centers and atrophy of lymphoid follicles, which may be associated to decrease of T cell number. Circulatory disturbs were reinforced by the presence of megakaryocytes in alveolar spaces, thrombus formation in glomerular capillaries and loss of endothelium in several tissues. Besides histopathological and ultrastructural observations, virus replication were investigated by detection of dengue antigens, especially the non-structural 3 protein (NS3), and confirmed by the presence of virus RNA negative strand (in situ hybridization), with second staining for identification of some cells. Results showed that dengue had broader tropism comparing to what was described before in literature, replicating in hepatocytes, type II pneumocytes and cardiac fibers, as well as in resident and circulating monocytes/macrophages and endothelial cells.

Dengue pathogenesis: a disease driven by the host response

Dengue viruses cause mild disease in the majority of infected individuals. In most cases, the disease is characterised by fever, headache, pain behind the eyes, muscle ache, joint pains, vomiting and diarrhoea. In a low percentage of patients, bleeding and loss of plasma (haemorrhage and plasma leakage) may occur. The hyper-permeability syndrome results in plasma leakage and, if the compensatory mechanisms of the body fail to control the plasma leakage or if medical intervention is late, shock may set in. Profound shock will subsequently lead to acidic blood (metabolic acidosis) and development of disseminated intravascular coagulation (DIC). During DIC multiple micro thromboses occur, leading to organ failure. The mechanisms governing pathogenesis of these forms of severe disease are not clear. High amounts of virus in the blood are believed to cause vascular fragility which, together with infection of endothelial cells and high levels of cytokines and other soluble mediators, may result in bleeding. In the absence of a correlation between the amount of virus in the blood and disease severity, it is likely that response to infection is an important cause of disease. The aberrant immune response to infection is believed to result in a cytokine storm, defined as an imbalance between cytokines driving an inflammation (pro-inflammatory) and those silencing an inflammation (anti-inflammatory). Several lines of evidence indicate that displacement of viral genotype and host genetic background are key factors driving the production of a cytokine storm. Several cytokines are known to induce apoptosis, a form of cell suicide (cause of haemorrhage), and/or affect adherens junctions (cause permeability) in vitro. Whether these cytokines may have such effects in vivo remains to be established.