Induced autophagy reduces virus output in dengue infected monocytic cells. Virology. 2011;418:74-84. [PMID: 21813150 DOI: 10.1016/j.virol.2011.07.010]

L-Dopa decarboxylase modulates autophagy in hepatocytes and is implicated in dengue virus-caused inhibition of autophagy completion

The enzyme L-Dopa Decarboxylase (DDC) synthesizes the catecholamine dopamine and the indolamine serotonin. Apart from its role in the brain as a neurotransmitter biosynthetic enzyme, DDC has been detected also in the liver and other peripheral organs, where it is implicated in cell proliferation, apoptosis, and host-virus interactions. Dengue virus (DENV) suppresses DDC expression at the later stages of infection, during which DENV also inhibits autophagosome-lysosome fusion. As dopamine affects autophagy in neuronal cells, we investigated the possible association of DDC with autophagy in human hepatocytes and examined whether DDC mediates the relationship between DENV infection and autophagy. We performed DDC silencing/overexpression and evaluated autophagic markers upon induction of autophagy, or suppression of autophagosome-lysosome fusion. Our results showed that DDC favored the autophagic process, at least in part, through its biosynthetic function, while knockdown of DDC or inhibition of DDC enzymatic activity prevented autophagy completion. In turn, autophagy induction upregulated DDC, while autophagy reduction by chemical or genetic (ATG14L knockout) ways caused the opposite effect. This study also implicated DDC with the cellular energetic status, as DDC silencing reduced the oxidative phosphorylation activity of the cell. We also report that upon DDC silencing, the repressive effect of DENV on the completion of autophagy was enhanced, and the inhibition of autolysosome formation did not exert an additive effect on viral proliferation. These data unravel a novel role of DDC in the autophagic process and suggest that DENV downregulates DDC expression to inhibit the completion of autophagy, reinforcing the importance of this protein in viral infections.

Autophagy Activation Induces p62-Dependent Autophagic Degradation of Dengue Virus Capsid Protein During Infection

In the past decade, dengue virus infection is one of the most prevalent and rapidly spreading arthropod-borne diseases worldwide with about 400 million infections every year. Although it has been reported that the dengue virus could take advantage of autophagy to promote its propagation, the association between selective autophagy and the dengue virus remains largely unclear. Here, we demonstrated that dengue virus capsid protein, the key viral protein for virus assembly, maturation, and replication, underwent autophagic degradation after autophagy activation. Autophagy cargo receptor p62 delivered ubiquitinated capsid protein to autophagosomes for degradation, which could be enhanced by Torin 1 treatments. Further study revealed that the association between p62 and viral capsid protein was dependent on the ubiquitin-binding domain of p62, and the poly-ubiquitin conjugated at lysine 76 of capsid protein served as a recognition signal for autophagy. Consistently, p62 deficiency in Huh7 cells led to the enhancement of dengue virus replication. Our study revealed that p62 targeted dengue virus capsid protein for autophagic degradation in a ubiquitin-dependent manner, which might uncover the potential roles of p62 in restricting dengue virus replication.

The Interplay between Autophagy and Virus Pathogenesis—The Significance of Autophagy in Viral Hepatitis and Viral Hemorrhagic Fevers

Autophagy is a process focused on maintaining the homeostasis of organisms; nevertheless, the role of this process has also been widely documented in viral infections. Thus, xenophagy is a selective form of autophagy targeting viruses. However, the relation between autophagy and viruses is ambiguous—this process may be used as a strategy to fight with a virus, but is also in favor of the virus’s replication. In this paper, we have gathered data on autophagy in viral hepatitis and viral hemorrhagic fevers and the relations impacting its viral pathogenesis. Thus, autophagy is a potential therapeutic target, but research is needed to fully understand the mechanisms by which the virus interacts with the autophagic machinery. These studies must be performed in specific research models other than the natural host for many reasons. In this paper, we also indicate Lagovirus europaeus virus as a potentially good research model for acute liver failure and viral hemorrhagic disease.

A Decade of Mighty Lipophagy: What We Know and What Facts We Need to Know?

Lipids are integral cellular components that act as substrates for energy provision, signaling molecules, and essential constituents of biological membranes along with a variety of other biological functions. Despite their significance, lipid accumulation may result in lipotoxicity, impair autophagy, and lysosomal function that may lead to certain diseases and metabolic syndromes like obesity and even cell death. Therefore, these lipids are continuously recycled and redistributed by the process of selective autophagy specifically termed as lipophagy. This selective form of autophagy employs lysosomes for the maintenance of cellular lipid homeostasis. In this review, we have reviewed the current literature about how lipid droplets (LDs) are recruited towards lysosomes, cross-talk between a variety of autophagy receptors present on LD surface and lysosomes, and lipid hydrolysis by lysosomal enzymes. In addition to it, we have tried to answer most of the possible questions related to lipophagy regulation at different levels. Moreover, in the last part of this review, we have discussed some of the pathological states due to the accumulation of these LDs and their possible treatments under the light of currently available findings.

Activation of the autophagy pathway decreases dengue virus infection in Aedes aegypti cells

Background

Mosquito-borne dengue virus (DENV) causes major disease worldwide, impacting 50–100 million people every year, and is spread by the major mosquito vector Aedes aegypti. Understanding mosquito physiology, including antiviral mechanisms, and developing new control strategies have become an important step towards the elimination of DENV disease. In the study reported here, we focused on autophagy, a pathway suggested as having a positive influence on virus replication in humans, as a potential antiviral target in the mosquito.

Methods

To understand the role played by autophagy in Ae. aegypti, we examined the activation of this pathway in Aag-2 cells, an Ae. aegypti-derived cell line, infected with DENV. Rapamycin and 3-methyladenine, two small molecules that have been shown to affect the function of the autophagy pathway, were used to activate or suppress, respectively, the autophagy pathway.

Results

At 1-day post-DENV infection in Aag-2 cells, transcript levels of both the microtubule-associated protein light chain 3-phosphatidylethanolamine conjugate (LC3-II) and autophagy-related protein 1 (ATG1) increased. Rapamycin treatment activated the autophagy pathway as early as 1-h post-treatment, and the virus titer had decreased in the Aag-2 cells at 2 days post-infection; in contrast, the 3-methyladenine treatment did not significantly affect the DENV titer. Treatment with these small molecules also impacted the ATG12 transcript levels in DENV-infected cells.

Conclusions

Our studies revealed that activation of the autophagy pathway through rapamycin treatment altered DENV infection in the mosquito cells, suggesting that this pathway could be a possible antiviral mechanism in the mosquito system. Here we provide fundamental information needed to proceed with future experiments and to improve our understanding of the mosquito’s immune response against DENV.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05066-w.

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.

Cell death pathways and viruses: Role of microRNAs

Viral infections lead to the death of more than a million people each year around the world, both directly and indirectly. Viruses interfere with many cell functions, particularly critical pathways for cell death, by affecting various intracellular mediators. MicroRNAs (miRNAs) are a major example of these mediators because they are involved in many (if not most) cellular mechanisms. Virus-regulated miRNAs have been implicated in three cell death pathways, namely, apoptosis, autophagy, and anoikis. Several molecules (e.g., BECN1 and B cell lymphoma 2 [BCL2] family members) are involved in both apoptosis and autophagy, while activation of anoikis leads to cell death similar to apoptosis. These mechanistic similarities suggest that common regulators, including some miRNAs (e.g., miR-21 and miR-192), are involved in different cell death pathways. Because the balance between cell proliferation and cell death is pivotal to the homeostasis of the human body, miRNAs that regulate cell death pathways have drawn much attention from researchers. miR-21 is regulated by several viruses and can affect both apoptosis and anoikis via modulating various targets, such as PDCD4, PTEN, interleukin (IL)-12, Maspin, and Fas-L. miR-34 can be downregulated by viral infection and has different effects on apoptosis, depending on the type of virus and/or host cell. The present review summarizes the existing knowledge on virus-regulated miRNAs involved in the modulation of cell death pathways. Understanding the mechanisms for virus-mediated regulation of cell death pathways could provide valuable information to improve the diagnosis and treatment of many viral diseases.

Transcriptome Analysis Reveals Downregulation of Urocortin Expression in the Hypothalamo-Neurohypophysial System of Spontaneously Hypertensive Rats

The chronically increased blood pressure characteristic of essential hypertension represents an insidious and cumulative risk for cardiovascular disease. Essential hypertension is a multifactorial condition, with no known specific aetiology but a strong genetic component. The Spontaneously Hypertensive rat (SHR) shares many characteristics of human essential hypertension, and as such is a commonly used experimental model. The mammalian hypothalamo-neurohypophyseal system (HNS) plays a pivotal role in the regulation of blood pressure, volume and osmolality. In order to better understand the possible role of the HNS in hypertension, we have used microarray analysis to reveal differential regulation of genes in the HNS of the SHR compared to a control normotensive strain, the Wistar Kyoto rat (WKY). These results were validated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). One of the genes identified and validated as being downregulated in SHR compared to WKY was that encoding the neuropeptide urocortin (Ucn). Immunohistochemical analyses revealed Ucn to be highly expressed within magnocellular neurons of the PVN and SON, with pronounced localisation in dendritic projections containing oxytocin and vasopressin. When Ucn was overexpressed in the PVN of the SHR by in vivo lentiviral mediated gene transfer, blood pressure was unaffected but there were significant, transient reductions in the VLF spectra of systolic blood pressure consistent with an action on autonomic balance. We suggest that Ucn may act, possibly via dendritic release, to subtly regulate neurohumoral aspects of arterial pressure control.

Systematic identification of autophagy-related proteins in Aedes albopictus

Autophagy is a conserved cellular process playing a role in maintenance of cellular homeostasis and response to changing nutrient conditions via degradation and recirculation of cellular redundant components. Autophagy-related proteins (Atg) play important function in autophagy pathway. Aedes albopictus mosquito is an effective vector transmitting multiple viruses which cause serious human diseases. Moreover, Aedes albopictus mosquito is becoming a serious threat to human health due to its widening distribution in recent years and thus worth of more research attention. It was reported that autophagy might play a role in viral infection in Aedes mosquito. To better understand the interaction between autophagy and arbovirus infection in mosquito system, it is necessary to identify autophagy pathway in the system. However, autophagy in Aedes albopictus mosquito is still poorly understood so far. We recently identified AaAtg8, the first Atg protein reported in Aedes albopictus mosquito. This work further identified twelve atg genes in Aedes albopictus mosquito. Sequence and phylogenetic analysis of the twelve atg genes were performed. Expression profiles of all the twelve Aaatg genes in different developmental stages and genders of Aedes albopictus mosquito were conducted. Effects of chemicals inhibiting or inducing autophagy on the levels of eight identified AaAtg proteins were examined. The function of two identified AaAtg proteins AaAtg6 and AaAtg16 and their response to arbovirus SINV infection were studied preliminarily. Taken together, this work systematically identified Aedes albopictus atg genes and provided basic information which might help to elucidate the autophagy pathway and the role of autophagy in arbovirus infection in Aedes mosquito system.

The Role of Autophagy-Mediated Dengue Virus Antibody-Dependent Enhancement Infection of THP-1 Cells

BACKGROUND

Antibody-dependent enhancement (ADE) of dengue virus (DENV) infection is identified as the main risk factor of severe dengue diseases. The underlying mechanisms leading to severe dengue fever remain unclear.

METHODS

THP-1 cells were treated with an autophagy inducer (rapamycin) or inhibitor (3-methyladenine [3-MA]) and infected with DENV and DENV-ADE. In order to investigate the expression profile of autophagy-related genes in DENV-ADE and DENV direct infection of THP-1 cells, the PCR array including 84 autophagy-related genes was selected to detect the expression of related genes, and then heat map and clustergram were established by analysis software to compare the expression differences of these genes between the DENV-ADE and DENV direct infection.

RESULTS

Autophagy-inducing complex related genes ATG5 and ATG12 were upregulated, and autophagosomes were also observed by transmission electron microscopy among DENV-ADE- and DENV-infected THP-1 cells, which indicated that autophagy was involved in dengue infection. The results show that 3-MA has a significant inhibitory effect on ATG12 in THP-1 cells; on the contrary, the expression of ATG12 was upreg-ulated in THP-1 cells that were treated with rapamycin. The autophagy-related genes ESR1, INS, BNIP3, FAS, TGM2, ATG9B, and DAPK1 exhibited significant differences between DENV-ADE and DENV direct infection groups.

CONCLUSION

In the present study, an additional mechanism of autophagy was inhibited by the autophagy inhibitor (3-MA) in DENV- and DENV-ADE-infected THP-1 cells. Our finding provided a clear link between autophagy and antibody-enhanced infection of DENV.

Roles of Macrophage Migration Inhibitory Factor in Dengue Pathogenesis: From Pathogenic Factor to Therapeutic Target

Dengue virus (DENV) infection is the most prevalent mosquito-borne viral infection and can lead to severe dengue hemorrhagic fever (DHF) and even life-threatening dengue shock syndrome (DSS). Although the cytokine storm has been revealed as a critical factor in dengue disease, the limited understanding of dengue immunopathogenesis hinders the development of effective treatments. Macrophage migration inhibitory factor (MIF) is a pleiotropic proinflammatory cytokine that mediates diverse immune responses, and the serum level of MIF positively correlates with disease severity in patients with dengue. MIF is involved in DENV replication and many pathological changes, such as vascular leakage, during DENV infection. In this paper, the pathogenic roles of MIF and the regulation of MIF secretion during DENV infection are reviewed. Furthermore, whether MIF is a potential therapeutic target against DENV infection is also discussed.

Role of autophagy during the replication and pathogenesis of common mosquito-borne flavi- and alphaviruses

Arboviruses that are transmitted to humans by mosquitoes represent one of the most important causes of febrile illness worldwide. In recent decades, we have witnessed a dramatic re-emergence of several mosquito-borne arboviruses, including dengue virus (DENV), West Nile virus (WNV), chikungunya virus (CHIKV) and Zika virus (ZIKV). DENV is currently the most common mosquito-borne arbovirus, with an estimated 390 million infections worldwide annually. Despite a global effort, no specific therapeutic strategies are available to combat the diseases caused by these viruses. Multiple cellular pathways modulate the outcome of infection by either promoting or hampering viral replication and/or pathogenesis, and autophagy appears to be one of them. Autophagy is a degradative pathway generally induced to counteract viral infection. Viruses, however, have evolved strategies to subvert this pathway and to hijack autophagy components for their own benefit. In this review, we will focus on the role of autophagy in mosquito-borne arboviruses with emphasis on DENV, CHIKV, WNV and ZIKV, due to their epidemiological importance and high disease burden.

The roles of apoptosis, autophagy and unfolded protein response in arbovirus, influenza virus, and HIV infections

Virus infection induces different cellular responses in infected cells. These include cellular stress responses like autophagy and unfolded protein response (UPR). Both autophagy and UPR are connected to programed cell death I (apoptosis) in chronic stress conditions to regulate cellular homeostasis via Bcl2 family proteins, CHOP and Beclin-1. In this review article we first briefly discuss arboviruses, influenza virus, and HIV and then describe the concepts of apoptosis, autophagy, and UPR. Finally, we focus upon how apoptosis, autophagy, and UPR are involved in the regulation of cellular responses to arboviruses, influenza virus and HIV infections. Abbreviation: AIDS: Acquired Immunodeficiency Syndrome; ATF6: Activating Transcription Factor 6; ATG6: Autophagy-specific Gene 6; BAG3: BCL Associated Athanogene 3; Bak: BCL-2-Anatagonist/Killer1; Bax; BCL-2: Associated X protein; Bcl-2: B cell Lymphoma 2x; BiP: Chaperon immunoglobulin heavy chain binding Protein; CARD: Caspase Recruitment Domain; cART: combination Antiretroviral Therapy; CCR5: C-C Chemokine Receptor type 5; CD4: Cluster of Differentiation 4; CHOP: C/EBP homologous protein; CXCR4: C-X-C Chemokine Receptor Type 4; Cyto c: Cytochrome C; DCs: Dendritic Cells; EDEM1: ER-degradation enhancing-a-mannosidase-like protein 1; ENV: Envelope; ER: Endoplasmic Reticulum; FasR: Fas Receptor;G2: Gap 2; G2/M: Gap2/Mitosis; GFAP: Glial Fibrillary Acidic Protein; GP120: Glycoprotein120; GP41: Glycoprotein41; HAND: HIV Associated Neurodegenerative Disease; HEK: Human Embryonic Kidney; HeLa: Human Cervical Epithelial Carcinoma; HIV: Human Immunodeficiency Virus; IPS-1: IFN-β promoter stimulator 1; IRE-1: Inositol Requiring Enzyme 1; IRGM: Immunity Related GTPase Family M protein; LAMP2A: Lysosome Associated Membrane Protein 2A; LC3: Microtubule Associated Light Chain 3; MDA5: Melanoma Differentiation Associated gene 5; MEF: Mouse Embryonic Fibroblast; MMP: Mitochondrial Membrane Permeabilization; Nef: Negative Regulatory Factor; OASIS: Old Astrocyte Specifically Induced Substrate; PAMP: Pathogen-Associated Molecular Pattern; PERK: Pancreatic Endoplasmic Reticulum Kinase; PRR: Pattern Recognition Receptor; Puma: P53 Upregulated Modulator of Apoptosis; RIG-I: Retinoic acid-Inducible Gene-I; Tat: Transactivator Protein of HIV; TLR: Toll-like receptor; ULK1: Unc51 Like Autophagy Activating Kinase 1; UPR: Unfolded Protein Response; Vpr: Viral Protein Regulatory; XBP1: X-Box Binding Protein 1.

TIM-1 As a Signal Receptor Triggers Dengue Virus-Induced Autophagy

Dengue virus (DENV) infection triggers the activation of autophagy to facilitate the viral replication cycle from various aspects. Although a number of stimulators are proposed to activate autophagy, none of them appears prior to the uncoating process. Given that T-cell immunoglobulin and mucin domain 1 (TIM-1) receptor is a putative DENV receptor and promotes apoptotic body clearance by autophagy induction, it raises the possibility that TIM-1 may participate in the activation of DENV-induced autophagy. In this study, confocal images first revealed the co-localization of TIM-1 with autophagosomes in DENV-induced autophagy rather than rapamycin-induced autophagy, suggesting the co-transportation of TIM-1 with DENV during infection. The treatment of siRNA to knockdown TIM-1 expression in DENV-infected GFP-microtubule-associated protein light chain 3 (LC3)-Huh7.5 cells revealed that TIM-1 is required not only for DENV cellular internalization but also for autophagy activation. Furthermore, knockdown p85, a subunit of phosphoinositide 3-kinases (PI3Ks), which is co-localized with TIM-1 at rab5-positive endosomes caused the reduction of autophagy, indicating that TIM-1-mediated DENV-induced autophagy requires p85. Taken together, the current study uncovered TIM-1 as a novel factor for triggering autophagy in DENV infection through TIM-1-p85 axis, in addition to serving as a DENV receptor.

Mycophenolic acid (MPA) modulates host cellular autophagy progression in sub genomic dengue virus-2 replicon cells

Cellular autophagy (Macrophagy) is a self-degradative process, executed through the network of autophagy associated genes (ATGs) encoded proteins. Both in vitro and in vivo studies suggest that dengue virus (DENV) induces autophagy and supports the viral genome replication and translation. Therefore, the cellular autophagy induced by dengue virus can be a good target for antiviral drug development. The action of mycophenolic acid (MPA), a specific inhibitor of DENV replication, was investigated in the stable BHK-21/DENV2 replicon cells. The inhibition was mediated by enhanced degradation of autophagic substrates in stable BHK-21/DENV2 replicon cells as evidenced by a decrease in lapidated LC3 (LC3II) and p62 expression in the presence of MPA. In contrast, the results indicated that four gene sets, namely Transmembrane protein 74 (TMEM74), Unc-51-like kinase 2 (ULK2), Cathepsin D (CTSD) and Estrogen receptor 1 (ESR1) were upregulated in stable BHK-21/DENV2 replicon cells, due to the sustained dynamic replication of DENV2 genome. These ATGs involved in the pre-autophagosomal structure (PAS) formation, were suppressed in the presence MPA. Instead, MPA induced the expression of different set of autophagy genes such as ATG4, AKT1, APP, ATG16L1, ATG16L2, B2M and HPRT1. An enzyme involved in the nucleotide salvage pathway, HPRT1, was highly expressed in the presence of MPA. The study shows that DENV2 replication is dependent on PAS formation and is inhibited in the presence of MPA by enhancing the degradation of autophagic substrates and suppression of PAS formation. This study provides impetus in designing MPA analogues to effectively inhibit dengue viral replication.

Significance of Autophagy in Dengue Virus Infection: A Brief Review

Dengue virus (DENV) causes asymptomatic to severe life-threatening infections and affects millions of people worldwide. Autophagy, a cellular degradative pathway, has both proviral and antiviral functions. Dengue virus triggers the autophagy pathway for the successful replication of its genome. However, the exact mechanism and the viral factors involved in activating this pathway remain unclear. This review summarizes the existing knowledge on the mechanism of autophagy induction and its significance during DENV infection.

The Multifaceted Roles of Autophagy in Flavivirus-Host Interactions

Autophagy is an evolutionarily conserved cellular process in which intracellular components are eliminated via lysosomal degradation to supply nutrients for organelle biogenesis and metabolic homeostasis. Flavivirus infections underlie multiple human diseases and thus exert an immense burden on public health worldwide. Mounting evidence indicates that host autophagy is subverted to modulate the life cycles of flaviviruses, such as hepatitis C virus, dengue virus, Japanese encephalitis virus, West Nile virus and Zika virus. The diverse interplay between autophagy and flavivirus infection not only regulates viral growth in host cells but also counteracts host stress responses induced by viral infection. In this review, we summarize the current knowledge on the role of autophagy in the flavivirus life cycle. We also discuss the impacts of virus-induced autophagy on the pathogeneses of flavivirus-associated diseases and the potential use of autophagy as a therapeutic target for curing flavivirus infections and related human diseases.

Blockade of Rostral Ventrolateral Medulla Apelin Receptors Does Not Attenuate Arterial Pressure in SHR and L-NAME-Induced Hypertensive Rats

Dysfunction of the apelinergic system, comprised of the neuropeptide apelin mediating its effects via the G protein-coupled apelin receptor (APJ), may underlie the onset of cardiovascular disease such as hypertension. Apelin expression is increased in the rostral ventrolateral medulla (RVLM) in spontaneously hypertensive rats (SHRs) compared to Wistar-Kyoto (WKY) normotensive rats, however, evidence that the apelinergic system chronically influences mean arterial blood pressure (MABP) under pathophysiological conditions remains to be established. In this study we investigated, in conscious unrestrained rats, whether APJ contributes to MABP and sympathetic vasomotor tone in the progression of two models of hypertension - SHR and _L-NAME-treated rats - and whether APJ contributes to the development of hypertension in pre-hypertensive SHR. In SHR we showed that APJ gene (aplnr) expression was elevated in the RVLM, and there was a greater MABP increase following microinjection of [Pyr¹]apelin-13 to the RVLM of SHR compared to WKY rats. Bilateral microinjection of a lentiviral APJ-specific-shRNA construct into the RVLM of WKY, SHR, and _L-NAME-treated rats, chronically implanted with radiotelemeters to measure MABP, decreased aplnr expression in the RVLM and abolished acute [Pyr¹]apelin-13-induced increases in MABP. However, chronic knockdown of aplnr in the RVLM did not affect MABP in either SHR or _L-NAME-treated rats. Moreover, knockdown of aplnr in the RVLM of prehypertensive SHR did not protect against the development of hypertension. These results show that endogenous apelin, acting via APJ, is not involved in the genesis or maintenance of hypertension in either animal model used in this study.

Dengue virus and the host innate immune response

Dengue virus (DENV) is a mosquito-borne Flavivirus that is endemic in many tropical and sub-tropical countries where the transmission vectors Aedes spp. mosquitoes resides. There are four serotypes of the virus. Each serotype is antigenically different, meaning they elicit heterologous antibodies. Infection with one serotype will create neutralizing antibodies to the serotype. Cross-protection from other serotypes is not long term, instead heterotypic infection can cause severe disease. This review will focus on the innate immune response to DENV infection and the virus evasion of the innate immune system by escaping recognition or inhibiting the production of an antiviral state. Activated innate immune pathways includes type I interferon, complement, apoptosis, and autophagy, which the virus can evade or exploit to exacerbate disease. It is important to understand out how the immune system reacts to infection and how the virus evades immune response in order to develop effective antivirals and vaccines.

Subverting the mechanisms of cell death: flavivirus manipulation of host cell responses to infection

Viruses exploit host metabolic and defence machinery for their own replication. The flaviviruses, which include Dengue (DENV), Yellow Fever (YFV), Japanese Encephalitis (JEV), West Nile (WNV) and Zika (ZIKV) viruses, infect a broad range of hosts, cells and tissues. Flaviviruses are largely transmitted by mosquito bites and humans are usually incidental, dead-end hosts, with the notable exceptions of YFV, DENV and ZIKV. Infection by flaviviruses elicits cellular responses including cell death via necrosis, pyroptosis (involving inflammation) or apoptosis (which avoids inflammation). Flaviviruses exploit these mechanisms and subvert them to prolong viral replication. The different effects induced by DENV, WNV, JEV and ZIKV are reviewed. Host cell surface proteoglycans (PGs) bearing glycosaminoglycan (GAG) polysaccharides — heparan/chondroitin sulfate (HS/CS) — are involved in initial flavivirus attachment and during the expression of non-structural viral proteins play a role in disease aetiology. Recent work has shown that ZIKV-infected cells are protected from cell death by exogenous heparin (a GAG structurally similar to host cell surface HS), raising the possibility of further subtle involvement of HS PGs in flavivirus disease processes. The aim of this review is to synthesize information regarding DENV, WNV, JEV and ZIKV from two areas that are usually treated separately: the response of host cells to infection by flaviviruses and the involvement of cell surface GAGs in response to those infections.

miR-146a Inhibits dengue-virus-induced autophagy by targeting TRAF6

During dengue virus (DENV) infection, the virus manipulates different cellular pathways to assure productive replication, including autophagy. However, it remains unclear how this autophagic process is regulated. Here, we have demonstrated a novel role for the microRNA miR-146a in negatively regulating the cellular autophagic pathway in DENV-infected A549 cells and THP-1 cells. Overexpression of miR-146a significantly blocked DENV2-induced autophagy, and LNA-mediated inhibition of miR-146a counteracted these effects. Moreover, co-overexpression of TRAF6, a target of miR-146a, significantly reversed the inhibitory effect of miR-146a on autophagy. Notably, treatment with recombinant IFN-β fully restored the autophagic activity in TRAF6-silenced cells. Furthermore, our data showed that, in DENV2-infected A549 cells, autophagy promoted a pro-inflammatory response to significantly increase TNF-α and IL-6 production. Taken together, our results define a novel role for miR-146a as a negative regulator of DENV-induced autophagy and identify TRAF6 as a key target of this microRNA in modulating the DENV-autophagy interaction.

miR-21 promotes dengue virus serotype 2 replication in HepG2 cells

Infection with the mosquito transmitted dengue virus (DENV) remains a significant worldwide public health problem. While the majority of infections are asymptomatic, infection can result in a range of symptoms. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression through repression or degradation of mRNAs. To understand the contribution of miRNAs to DENV 2 replication, we screened a number of candidate miRNAs for variations in expression levels during DENV 2 infection of HepG2 (liver) cells. Seven miRNAs were identified as differentially expressed, and one, miR-21, was differentially expressed at all time points examined. Interestingly, miR-21 was also differentially regulated in DENV 2 infection under conditions of antibody dependent enhancement of infection, and in direct Zika virus infection, but not in DENV 4 infection. The role of miR-21 during DENV infection was further examined by treating HepG2 cells with an anti-miR-21 (AMO-21) before DENV infection. The results showed a significant reduction in DENV 2 production, clearly suggesting that miR-21 plays a key role in DENV 2 replication. To further confirm the role of miR-21 in DENV infection, a peptide nucleic acid-21 (PNA-21) construct with a nucleotide sequence complementary to AMO-21, was co-administered with AMO-21 as an AMO-21/PNA-21 complex followed by DENV 2 infection. The results showed that AMO-21 significantly reduced DENV 2 titer, PNA-21 significantly increased DENV 2 titer and the combined AMO-21/PNA-21 showed no difference from non-treated infection controls. Taken together, the results show that miR-21 promotes DENV 2 replication, and this mechanism could serve as a possible therapeutic intervention point.

Autophagy-associated dengue vesicles promote viral transmission avoiding antibody neutralization

One of the major defense mechanisms against virus spread in vivo is the blocking of viral infectibility by neutralizing antibodies. We describe here the identification of infectious autophagy-associated dengue vesicles released from infected cells. These vesicles contain viral proteins E, NS1, prM/M, and viral RNA, as well as host lipid droplets and LC3-II, an autophagy marker. The viral RNA can be protected within the autophagic organelles since anti-dengue neutralizing antibodies do not have an effect on the vesicle-mediated transmission that is able to initiate a new round of infection in target cells. Importantly, such infectious vesicles were also detected in a patient serum. Our study suggests that autophagy machinery plays a new role in dengue virus transmission. This discovery explains the inefficiency of neutralizing antibody upon dengue infection as a potential immune evasion mechanism in vivo.

Nevirapine induces apoptosis in liver (HepG2) cells

OBJECTIVE

To generate insights into the mechanism of NVP induced hepatotoxicity.

METHODS

Liver (HepG2) cells were cultured with various concentrations of NVP. This cell line was chosen because it has low expression of cytochrome P450, allowing evaluation of the effects of NVP rather than specific metabolites. Cytotoxicity was determined using a proliferation assay and cell numbers were monitored using trypan blue exclusion assay for long term culture experiments and apoptosis induction was determined by morphological and biochemical investigation.

RESULTS

HepG2 cells treated with the highest concentration of NVP tested (819 μM) initially showed a rounded morphology and all cells had died by week three of exposure. Nuclear condensation and fragmentation, increased Annexin V/propidium iodide staining and caspase 9 activation all supported the induction of apoptosis in HepG2 cells in response to NVP treatment.

CONCLUSIONS

There is a clear induction of apoptosis in response to NVP which suggests that NVP has significant cytotoxicity, over and above any cytotoxicity of metabolites and may contribute directly to patient hepatotoxicity.

Dengue-induced autophagy, virus replication and protection from cell death require ER stress (PERK) pathway activation

A virus that reproduces in a host without killing cells can easily establish a successful infection. Previously, we showed that dengue-2, a virus that threatens 40% of the world, induces autophagy, enabling dengue to reproduce in cells without triggering cell death. Autophagy further protects the virus-laden cells from further insults. In this study, we evaluate how it does so; we show that dengue upregulates host pathways that increase autophagy, namely endoplasmic reticulum (ER) stress and ataxia telangiectasia mutated (ATM) signaling followed by production of reactive oxygen species (ROS). Inhibition of ER stress or ATM signaling abrogates the dengue-conferred protection against other cell stressors. Direct inhibition of ER stress response in infected cells decreases autophagosome turnover, reduces ROS production and limits reproduction of dengue virus. Blocking ATM activation, which is an early response to infection, decreases transcription of ER stress response proteins, but ATM has limited impact on production of ROS and virus titers. Production of ROS determines only late-onset autophagy in infected cells and is not necessary for dengue-induced protection from stressors. Collectively, these results demonstrate that among the multiple autophagy-inducing pathways during infection, ER stress signaling is more important to viral replication and protection of cells than either ATM or ROS-mediated signaling. To limit virus production and survival of dengue-infected cells, one must address the earliest phase of autophagy, induced by ER stress.

Antibody-dependent enhancement of dengue virus infection inhibits RLR-mediated Type-I IFN-independent signalling through upregulation of cellular autophagy

Antibody dependent enhancement (ADE) of dengue virus (DENV) infection is identified as the main risk factor of severe Dengue diseases. Through opsonization by subneutralizing or non-neutralizing antibodies, DENV infection suppresses innate cell immunity to facilitate viral replication. However, it is largely unknown whether suppression of type-I IFN is necessary for a successful ADE infection. Here, we report that both DENV and DENV-ADE infection induce an early ISG (NOS2) expression through RLR-MAVS signalling axis independent of the IFNs signaling. Besides, DENV-ADE suppress this early antiviral response through increased autophagy formation rather than induction of IL-10 secretion. The early induced autophagic proteins ATG5-ATG12 participate in suppression of MAVS mediated ISGs induction. Our findings suggest a mechanism for DENV to evade the early antiviral response before IFN signalling activation. Altogether, these results add knowledge about the complexity of ADE infection and contribute further to research on therapeutic strategies.

Apoptosis, autophagy and unfolded protein response pathways in Arbovirus replication and pathogenesis

Arboviruses are pathogens that widely affect the health of people in different communities around the world. Recently, a few successful approaches toward production of effective vaccines against some of these pathogens have been developed, but treatment and prevention of the resulting diseases remain a major health and research concern. The arbovirus infection and replication processes are complex, and many factors are involved in their regulation. Apoptosis, autophagy and the unfolded protein response (UPR) are three mechanisms that are involved in pathogenesis of many viruses. In this review, we focus on the importance of these pathways in the arbovirus replication and infection processes. We provide a brief introduction on how apoptosis, autophagy and the UPR are initiated and regulated, and then discuss the involvement of these pathways in regulation of arbovirus pathogenesis.

Biology of Zika Virus Infection in Human Skin Cells

Zika virus (ZIKV) is an emerging arbovirus of the Flaviviridae family, which includes dengue, West Nile, yellow fever, and Japanese encephalitis viruses, that causes a mosquito-borne disease transmitted by the Aedes genus, with recent outbreaks in the South Pacific. Here we examine the importance of human skin in the entry of ZIKV and its contribution to the induction of antiviral immune responses. We show that human dermal fibroblasts, epidermal keratinocytes, and immature dendritic cells are permissive to the most recent ZIKV isolate, responsible for the epidemic in French Polynesia. Several entry and/or adhesion factors, including DC-SIGN, AXL, Tyro3, and, to a lesser extent, TIM-1, permitted ZIKV entry, with a major role for the TAM receptor AXL. The ZIKV permissiveness of human skin fibroblasts was confirmed by the use of a neutralizing antibody and specific RNA silencing. ZIKV induced the transcription of Toll-like receptor 3 (TLR3), RIG-I, and MDA5, as well as several interferon-stimulated genes, including OAS2, ISG15, and MX1, characterized by strongly enhanced beta interferon gene expression. ZIKV was found to be sensitive to the antiviral effects of both type I and type II interferons. Finally, infection of skin fibroblasts resulted in the formation of autophagosomes, whose presence was associated with enhanced viral replication, as shown by the use of Torin 1, a chemical inducer of autophagy, and the specific autophagy inhibitor 3-methyladenine. The results presented herein permit us to gain further insight into the biology of ZIKV and to devise strategies aiming to interfere with the pathology caused by this emerging flavivirus.

IMPORTANCE

Zika virus (ZIKV) is an arbovirus belonging to the Flaviviridae family. Vector-mediated transmission of ZIKV is initiated when a blood-feeding female Aedes mosquito injects the virus into the skin of its mammalian host, followed by infection of permissive cells via specific receptors. Indeed, skin immune cells, including dermal fibroblasts, epidermal keratinocytes, and immature dendritic cells, were all found to be permissive to ZIKV infection. The results also show a major role for the phosphatidylserine receptor AXL as a ZIKV entry receptor and for cellular autophagy in enhancing ZIKV replication in permissive cells. ZIKV replication leads to activation of an antiviral innate immune response and the production of type I interferons in infected cells. Taken together, these results provide the first general insights into the interaction between ZIKV and its mammalian host.

Evidence of plasticity in the dengue virus: Host cell interaction

Dengue virus (DENV) is the most important mosquito transmitted human viral pathogen. There are four different dengue viruses (DENV 1 to DENV 4) with multiple genotypes and strains. Whether there are significant differences in how these DENVs interact with and modulate the host cell proteome remains unclear. Using a panel of 12 DENVs representative of one isolate for each DENV from three different origins (lab adapted, low passage isolates from dengue fever patients, low passage isolates from dengue hemorrhagic fever patients) LLC-MK2 cells were equally infected and proteomic alterations compared by MALDI-TOF and principal component analysis and a sub-10 kDa peptidome analysis. There was no clear segregation of data with respect to either virus origin or serotype in either the MALDI-TOF or the peptidome analysis. The two isolates with the greatest variation from the other isolates in the MALDI-TOF analysis were a low passage DENV 3 dengue fever isolate and a low passage DENV 4 dengue hemorrhagic fever isolate. Analysis of the sub-10 kda protein fraction by LC-MS/MS identified 128 proteins of which only 28 (20%) were constantly expressed in all infections, while 80% showed variable expression, with no clear relationship with either serotype or virus origin. These results suggest that the interaction between DENV and the host cell is characterized by a degree of plasticity, whereby the end biological processes are not rigorously determined by specific proteome alterations, and that virus strain plays a role in determining the specific proteome changes.

Osmoregulation requires brain expression of the renal Na-K-2Cl cotransporter NKCC2

The Na-K-2Cl cotransporter 2 (NKCC2) was thought to be kidney specific. Here we show expression in the brain hypothalamo-neurohypophyseal system (HNS), wherein upregulation follows osmotic stress. The HNS controls osmotic stability through the synthesis and release of the neuropeptide hormone, arginine vasopressin (AVP). AVP travels through the bloodstream to the kidney, where it promotes water conservation. Knockdown of HNS NKCC2 elicited profound effects on fluid balance following ingestion of a high-salt solution-rats produced significantly more urine, concomitant with increases in fluid intake and plasma osmolality. Since NKCC2 is the molecular target of the loop diuretics bumetanide and furosemide, we asked about their effects on HNS function following disturbed water balance. Dehydration-evoked GABA-mediated excitation of AVP neurons was reversed by bumetanide, and furosemide blocked AVP release, both in vivo and in hypothalamic explants. Thus, NKCC2-dependent brain mechanisms that regulate osmotic stability are disrupted by loop diuretics in rats.

Autophagy facilitates antibody-enhanced dengue virus infection in human pre-basophil/mast cells

BACKGROUND

Dengue virus (DENV) infection can cause severe hemorrhagic disease in humans. Although the pathogenic mechanisms underlying severe DENV disease remain unclear, one of the possible contributing factors is antibody-dependent enhancement (ADE) which occurs when sub-neutralizing antibodies derived from a previous DENV infection enhance viral infection through interaction between virus-antibody complexes and FcR-bearing cells, such as macrophages and basophil/mast cells. Although recent reports showed that DENV induces autophagy, the relationship between antibody-enhanced DENV infection and autophagy is not clear.

METHODOLOGY/PRINCIPAL FINDINGS

We showed that sub-neutralizing antibodies derived from dengue patient sera enhanced DENV infection and autophagy in the KU812 pre-basophil-like cell line as well as the HMC-1 immature mast cell line. Antibody-enhanced DENV infection of KU812 cells increased the number of autophagosome vesicles, LC3 punctation, LC3-II accumulation, and p62 degradation over that seen in cells infected with DENV alone. The percentages of DENV envelope (E) protein-positive cells and LC3 puncta following antibody-enhanced DENV infection of KU812 cells were reduced by the autophagy inhibitor 3-MA. Antibody-enhanced DENV infection of HMC-1 cells showed co-localization of DENV E protein and dsRNA with autophagosomes, which was inhibited by 3-MA treatment. Furthermore, DENV infection and replication were reduced when KU812 cells were transfected with the autophagy-inhibiting Atg4BC74A mutant.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate a significant induction of autophagy in antibody-enhanced DENV infection of pre-basophil-like KU812 and immature mast cell-like HMC-1 cells. Also, autophagy plays an important role in DENV infection and replication in these cells. Given the importance of ADE and FcR-bearing cells such as monocytes, macrophages and basophil/mast cells in dengue disease, the results provide insights into dengue pathogenesis and therapeutic means of control.

Overexpression of corticotropin releasing factor in the central nucleus of the amygdala advances puberty and disrupts reproductive cycles in female rats

Prolonged exposure to environmental stress activates the hypothalamic-pituitary-adrenal (HPA) axis and generally disrupts the hypothalamic-pituitary-gonadal axis. Because CRF expression in the central nucleus of the amygdala (CeA) is a key modulator in adaptation to chronic stress, and central administration of CRF inhibits the hypothalamic GnRH pulse generator, we tested the hypothesis that overexpression of CRF in the CeA of female rats alters anxiety behavior, dysregulates the HPA axis response to stress, changes pubertal timing, and disrupts reproduction. We used a lentiviral vector to increase CRF expression site specifically in the CeA of preweaning (postnatal day 12) female rats. Overexpression of CRF in the CeA increased anxiety-like behavior in peripubertal rats shown by a reduction in time spent in the open arms of the elevated plus maze and a decrease in social interaction. Paradoxically, puberty onset was advanced but followed by irregular estrous cyclicity and an absence of spontaneous preovulatory LH surges associated with proestrous vaginal cytology in rats overexpressing CRF. Despite the absence of change in basal corticosterone secretion or induced by stress (lipopolysaccharide or restraint), overexpression of CRF in the CeA significantly decreased lipopolysaccharide, but not restraint, stress-induced suppression of pulsatile LH secretion in postpubertal ovariectomized rats, indicating a differential stress responsivity of the GnRH pulse generator to immunological stress and a potential adaptation of the HPA axis to chronic activation of amygdaloid CRF. These data suggest that the expression profile of this key limbic brain CRF system might contribute to the complex neural mechanisms underlying the increasing incidence of early onset of puberty on the one hand and infertility on the other attributed to chronic stress in modern human society.

Revisiting dengue virus-host cell interaction: new insights into molecular and cellular virology

Dengue virus (DENV) is an emerging mosquito-borne human pathogen that affects millions of individuals each year by causing severe and potentially fatal syndromes. Despite intense research efforts, no approved vaccine or antiviral therapy is yet available. Overcoming this limitation requires detailed understanding of the intimate relationship between the virus and its host cell, providing the basis to devise optimal prophylactic and therapeutic treatment options. With the advent of novel high-throughput technologies including functional genomics, transcriptomics, proteomics, and lipidomics, new important insights into the DENV replication cycle and the interaction of this virus with its host cell have been obtained. In this chapter, we provide a comprehensive overview on the current status of the DENV research field, covering every step of the viral replication cycle with a particular focus on virus-host cell interaction. We will also review specific chemical inhibitors targeting cellular factors and processes of relevance for the DENV replication cycle and their possible exploitation for the development of next generation antivirals.

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.

Autophagy in hepatitis C virus-host interactions: potential roles and therapeutic targets for liver-associated diseases

Autophagy is a lysosome-associated, degradative process that catabolizes cytosolic components to recycle nutrients for further use and maintain cell homeostasis. Hepatitis C virus (HCV) is a major cause of chronic hepatitis, which often leads to end-stage liver-associated diseases and is a significant burden on worldwide public health. Emerging lines of evidence indicate that autophagy plays an important role in promoting the HCV life cycle in host cells. Moreover, the diverse impacts of autophagy on a variety of signaling pathways in HCV-infected cells suggest that the autophagic process is required for balancing HCV-host cell interactions and involved in the pathogenesis of HCV-related liver diseases. However, the detailed molecular mechanism underlying how HCV activates autophagy to benefit viral growth is still enigmatic. Additionally, how the autophagic response contributes to disease progression in HCV-infected cells remains largely unknown. Hence, in this review, we overview the interplay between autophagy and the HCV life cycle and propose possible mechanisms by which autophagy may promote the pathogenesis of HCV-associated chronic liver diseases. Moreover, we outline the related studies on how autophagy interplays with HCV replication and discuss the possible implications of autophagy and viral replication in the progression of HCV-induced liver diseases, e.g., steatosis and hepatocellular carcinoma. Finally, we explore the potential therapeutics that target autophagy to cure HCV infection and its related liver diseases.

Transcription factor CREB3L1 regulates vasopressin gene expression in the rat hypothalamus

Arginine vasopressin (AVP) is a neurohypophysial hormone regulating hydromineral homeostasis. Here we show that the mRNA encoding cAMP responsive element-binding protein-3 like-1 (CREB3L1), a transcription factor of the CREB/activating transcription factor (ATF) family, increases in expression in parallel with AVP expression in supraoptic nuclei (SONs) and paraventicular nuclei (PVNs) of dehydrated (DH) and salt-loaded (SL) rats, compared with euhydrated (EH) controls. In EH animals, CREB3L1 protein is expressed in glial cells, but only at a low level in SON and PVN neurons, whereas robust upregulation in AVP neurons accompanied DH and SL rats. Concomitantly, CREB3L1 is activated by cleavage, with the N-terminal domain translocating from the Golgi, via the cytosol, to the nucleus. We also show that CREB3L1 mRNA levels correlate with AVP transcription level in SONs and PVNs following sodium depletion, and as a consequence of diurnal rhythm in the suprachiasmatic nucleus. We tested the hypothesis that CREB3L1 activates AVP gene transcription. Both full-length and constitutively active forms of CREB3L1 (CREB3L1CA) induce the expression of rat AVP promoter-luciferase reporter constructs, whereas a dominant-negative mutant reduces expression. Rat AVP promoter deletion constructs revealed that CRE-like and G-box sequences in the region between -170 and -120 bp are important for CREB3L1 actions. Direct binding of CREB3L1 to the AVP promoter was shown by chromatin immunoprecipitation both in vitro and in the SON itself. Injection of a lentiviral vector expressing CREB3L1CA into rat SONs and PVNs resulted in increased AVP biosynthesis. We thus identify CREB3L1 as a regulator of AVP transcription in the rat hypothalamus.

Role of intracellular events in the pathogenesis of dengue; an overview

Dengue is one of the most important mosquito-borne viral diseases that are relentlessly spreading in newer areas in the tropical and subtropical regions of the World. In last fifty years, in spite of intensive and extensive investigations, pathogenesis of dengue is still not clearly understood. Recently, the research focus is on studying the role of intracellular events in pathogenesis of viral infections. Entry of virion in the host cell is followed by quick succession of events, unfolded protein response, lipid bodies and lipophagy, endoplasmic reticulum stress and recent demonstration of autophagy. The turbulence caused by these events may result in clearance of the virus/enhanced replication and survival of the host cell/apoptosis. Both, increased virus load and apoptosis of host cell may have pathological effects on the host. In the present review, we have summed up the role of various intracellular events in viral infections with special emphasis on Dengue virus infection.

Dengue 2 infection of HepG2 liver cells results in endoplasmic reticulum stress and induction of multiple pathways of cell death

BACKGROUND

A number of studies have implicated the direct involvement of the liver in dengue virus (DENV) infection, and it has been widely shown that liver cells subsequently undergo apoptosis. The mechanism by which liver cells undergo apoptosis in response to DENV infection remains unclear. To provide further information on the mechanism of apoptosis in DENV infected liver cells, HepG2 cells were infected with DENV 2 and analyzed for the induction of ER stress, apoptosis and autophagy.

RESULTS

In response to DENV infection, HepG2 cells showed the induction of both the ER resident unfolded protein response as well as the Noxa/PUMA stress response pathways. Proteolytic activation of caspases 4, 7, 8 and 9 was observed as well as changes in mitochondrial transmembrane potential. Increased monodansylcadaverine staining was observed in DENV infected cells, consistent with the previously reported induction of autophagy.

CONCLUSIONS

These results are consistent with a model in which the induction of multiple ER stress pathways is coupled with the induction of multiple cell death pathways as a mechanism to ensure the removal of infected liver cells from the system.

Temporal dynamics of the transcriptional response to dengue virus infection in Nicaraguan children

Dengue is the most prevalent mosquito-borne human illness worldwide. The ability to predict disease severity during the earliest days of the illness is a long-sought, but unachieved goal.

We examined human genome-wide transcript abundance patterns in daily peripheral blood mononuclear cell (PBMC) samples from 41 children hospitalized with dengue virus (DENV) infection in Nicaragua, as well as 8 healthy control subjects. Nine patients had primary dengue fever (DF1), 11 had dengue fever with serologic evidence of prior DENV infection, i.e., secondary dengue fever (DF2), 12 had dengue hemorrhagic fever (DHF), and 9 had dengue shock syndrome (DSS). We identified 2,092 genes for which transcript abundance differed significantly between patients on days 3–6 of fever and healthy subjects (FDR<1%). Prior DENV infection explained the greatest amount of variation in gene expression among patients. The number of differentially expressed genes was greatest on fever day 3 in patients with DF1, while the number in patients with DF2 or DHF/DSS was greatest on day 5. Genes associated with the mitotic cell cycle and B cell differentiation were expressed at higher levels, and genes associated with signal transduction and cell adhesion were expressed at lower levels, in patients versus healthy controls. On fever day 3, a set of interferon-stimulated gene transcripts was less abundant in patients who subsequently developed DSS than in other patient groups (p<0.05, ranksum). Patients who later developed DSS also had higher levels of transcripts on day 3 associated with mitochondrial function (p<0.01, ranksum). These day 3 transcript abundance findings were not evident on subsequent fever days.

In conclusion, we identified differences in the timing and magnitude of human gene transcript abundance changes in DENV patients that were associated with serologic evidence of prior infection and with disease severity. Some of these differential features may predict the outcome of DENV infection.

Infection with dengue virus (DENV) causes dengue fever, the most prevalent mosquito-borne illness of humans worldwide. Tens of millions of cases occur annually; up to 500,000 patients develop additional life-threatening complications, including hemorrhage and shock. The clinical course of the disease evolves rapidly, making it difficult to identify patients at risk for severe disease and suggesting that biological events associated with the development of severe disease may be short-lived. We examined gene expression patterns in the blood of children hospitalized with DENV infection, and found that patients with differences in disease severity and history of previous DENV infection shared a common set of gene expression features, but the timing and magnitude of these features differed. In our study, prior DENV infection explained the greatest amount of variation in gene expression among patients. We discovered features of gene expression on day 3 that were associated with subsequent disease severity—features that were not apparent on subsequent days, emphasizing the importance of looking at temporal patterns of gene expression in acute infection.

Subversion of autophagy in adherent invasive Escherichia coli-infected neutrophils induces inflammation and cell death

Invading bacteria are recognized, captured and killed by a specialized form of autophagy, called xenophagy. Recently, defects in xenophagy in Crohn’s disease (CD) have been implicated in the pathogenesis of human chronic inflammatory diseases of uncertain etiology of the gastrointestinal tract. We show here that pathogenic adherent-invasive Escherichia coli (AIEC) isolated from CD patients are able to adhere and invade neutrophils, which represent the first line of defense against bacteria. Of particular interest, AIEC infection of neutrophil-like PLB-985 cells blocked autophagy at the autolysosomal step, which allowed intracellular survival of bacteria and exacerbated interleukin-8 (IL-8) production. Interestingly, this block in autophagy correlated with the induction of autophagic cell death. Likewise, stimulation of autophagy by nutrient starvation or rapamycin treatment reduced intracellular AIEC survival and IL-8 production. Finally, treatment with an inhibitor of autophagy decreased cell death of AIEC-infected neutrophil-like PLB-985 cells. In conclusion, excessive autophagy in AIEC infection triggered cell death of neutrophils.

Hepatitis C virus and cellular stress response: implications to molecular pathogenesis of liver diseases

Infection with hepatitis C virus (HCV) is a leading risk factor for chronic liver disease progression, including steatosis, cirrhosis, and hepatocellular carcinoma. With approximately 3% of the human population infected worldwide, HCV infection remains a global public health challenge. The efficacy of current therapy is still limited in many patients infected with HCV, thus a greater understanding of pathogenesis in HCV infection is desperately needed. Emerging lines of evidence indicate that HCV triggers a wide range of cellular stress responses, including cell cycle arrest, apoptosis, endoplasmic reticulum (ER) stress/unfolded protein response (UPR), and autophagy. Also, recent studies suggest that these HCV-induced cellular responses may contribute to chronic liver diseases by modulating cell proliferation, altering lipid metabolism, and potentiating oncogenic pathways. However, the molecular mechanism underlying HCV infection in the pathogenesis of chronic liver diseases still remains to be determined. Here, we review the known stress response activation in HCV infection in vitro and in vivo, and also explore the possible relationship of a variety of cellular responses with the pathogenicity of HCV-associated diseases. Comprehensive knowledge of HCV-mediated disease progression shall shed new insights into the discovery of novel therapeutic targets and the development of new intervention strategy.

Regulation of lipid stores and metabolism by lipophagy

Intracellular lipids are stored in lipid droplets (LDs) and metabolized by cytoplasmic neutral hydrolases to supply lipids for cell use. Recently, an alternative pathway of lipid metabolism through the lysosomal degradative pathway of autophagy has been described and termed lipophagy. In this form of lipid metabolism, LD triglycerides (TGs) and cholesterol are taken up by autophagosomes and delivered to lysosomes for degradation by acidic hydrolases. Free fatty acids generated by lipophagy from the breakdown of TGs fuel cellular rates of mitochondrial β-oxidation. Lipophagy therefore functions to regulate intracellular lipid stores, cellular levels of free lipids such as fatty acids and energy homeostasis. The amount of lipid metabolized by lipophagy varies in response to the extracellular supply of nutrients. The ability of the cell to alter the amount of lipid targeted for autophagic degradation depending on nutritional status demonstrates that this process is selective. Intracellular lipids themselves regulate levels of autophagy by unclear mechanisms. Impaired lipophagy can lead to excessive tissue lipid accumulation such as hepatic steatosis, alter hypothalamic neuropeptide release to affect body mass, block cellular transdifferentiation and sensitize cells to death stimuli. Future studies will likely identify additional mechanisms by which lipophagy regulates cellular physiology, making this pathway a potential therapeutic target in a variety of diseases.

Interplay between the cellular autophagy machinery and positive-stranded RNA viruses

Autophagy is a conserved cellular process that acts as a key regulator in maintaining cellular homeostasis. Recent studies implicate an important role for autophagy in infection and immunity by removing invading pathogens and through modulating innate and adaptive immune responses. However, several pathogens, notably some positive-stranded RNA viruses, have subverted autophagy to their own ends. In this review, we summarize the current understanding of how viruses with a positive-stranded RNA genome interact with the host autophagy machinery to control their replication and spread. We review the mechanisms underlying the induction of autophagy and discuss the pro- and anti-viral functions of autophagy and the potential mechanisms involved.