Dengue virus-induced ER stress is required for autophagy activation, viral replication, and pathogenesis both in vitro and in vivo

The Impact of Vitamin D in the Prevention of Influenza, COVID-19, and Dengue: A Review

Since its discovery, vitamin D (VD) has been known for its implications in maintaining bone homeostasis. However, in recent years it has been discovered that the vitamin D receptor is expressed on different cells of the immune system and that these cells can locally produce the active form of this molecule, calcitriol, strongly suggesting that this vitamin might play a key role in both branches of the immune system, innate and adaptive. Recent evidence has demonstrated that VD participates in the different protective phases of the immune system against invading microorganisms, including in the activation and production of antimicrobial peptides, in the inactivation of replication of infectious agents, in the prevention of the exposure of cellular receptors to microbial adhesion, and, more importantly, in the modulation of the inflammatory response. In recent years, the world has witnessed major outbreaks of an ancient infectious disease, dengue fever; the emergence of a pandemic caused by an unknown virus, SARS-CoV-2; and the resurgence of a common respiratory infection, influenza. Despite belonging to different viral families, the etiological agents of these infections present a common trait: their capacity to cause complications not only through their cytopathic effect on target tissues but also through the excessive inflammatory response produced by the human host against an infection. This review outlines the current understanding of the role that vitamin D plays in the prevention of the aforementioned diseases and in the development of their complications through its active participation as a major modulator of the immune response.

Advances in Nanobiosensors for Rapid and Sensitive Detection of Dengue Virus Biomarkers by Using Clinical Laboratory

BACKGROUND

The recent rise in dengue virus (DENV) cases poses a significant threat to human health, with infections ranging from mild to severe and potentially leading to premature death.

OBJECTIVE

To highlight the importance of early detection of DENV and to review advancements in detection technologies, particularly focusing on nanobiosensors.

METHODS

This review examines traditional detection methods for DENV, including molecular, serological, and direct virus culture techniques, while discussing their limitations. It also explores innovative technologies that enhance detection accuracy, speed, and efficiency.

RESULTS

Nonstructural protein 1 (NS1) serves as a key biomarker present in high concentrations during the early stages of DENV infection, underscoring the need for timely detection. Traditional methods, while effective, have limitations that new technologies aim to address. Biosensors, particularly nanobiosensors, have emerged as promising tools for rapid, sensitive, and cost-effective DENV detection.

CONCLUSION

The adoption of advanced detection methods, especially nanobiosensors, is crucial for improving DENV management and reducing human suffering. This review provides a comprehensive overview of nanobiosensors and their applications, presented in an accessible manner for readers.

Seneca Valley virus induces mitochondrial apoptosis by activating ER stress or the PERK pathway based on Ca2+ transfer from ER to mitochondria

Seneca Valley virus (SVV), also known as Senecavirus A, a porcine pathogen that causes vesicular diseases, is prevalent in pig herds worldwide. SVV infection induces endoplasmic reticulum (ER) stress in PK-15 and BHK-21 cells, accompanied by activation of the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) and activating transcription factor 6 (ATF6) pathways, which in turn facilitates SVV replication. ER stress is associated with the regulation of Ca2+ homeostasis and mitochondrial apoptosis. However, the precise role of Ca2+ in SVV-induced apoptosis remains unclear. In this study, western blotting, flow cytometry, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) detection revealed that either ER stress or the PERK pathway is involved in the apoptosis of SVV-infected cells treated with specific inhibitors. Furthermore, SVV-mediated ER stress markedly contributed to the transfer of Ca2+ from the ER to mitochondria. The subsequent increase in mitochondrial Ca2+ content was accompanied by an increased number of ER membranes near the mitochondria. Finally, the inhibition of mitochondrial Ca2+ overload, ER stress, and the PERK pathway substantially attenuated SVV-mediated mitochondrial dysfunction, as evidenced by analyzing mitochondrial membrane potential (MMP), mitochondrial permeability transition poremPTP, reactive oxygen speciesROS, and adenosine 5'-triphosphate ATP, and the levels of mitochondrial apoptosis. These findings demonstrate that SVV induces mitochondrial apoptosis, which is dependent on ER stress-mediated transmission of Ca2+ from the ER to the mitochondria.

IMPORTANCE

Viruses have developed multiple mechanisms to facilitate their proliferation or persistence through manipulating various organelles in cells. Seneca Valley virus (SVV), as a novel emerging pathogen associated with vesicular disease, is clinically and economically important infections that affect farm animals. Previously, we had confirmed that SVV-induced endoplasmic reticulum (ER) stress benefited for viral replication. Ca2+, as an intracellular signaling messenger mainly stored in the ER, is regulated by ER stress and then involved in apoptosis. However, the precise mechanism that Ca2+ transfer induced by SVV infection triggered apoptosis remained unclear. Here, we found that SVV infection triggered the Ca2+ transform from ER to mitochondria, resulting in mitochondrial dysfunction, and finally induced mitochondrial apoptosis. Our study shed light on a novel mechanism revealing how ER stress manipulates Ca2+ homeostasis to induce mitochondrial apoptosis and regulate viral proliferation.

ATF6-mediated mild ER stress inhibits HBV transcription and replication, which is dependent on mTOR activation

Chronic hepatitis B (CHB) remains a serious global health problem. In our previous investigation, HBV was found to activate a mild ER stress, which facilitated the establishment of persistent HBV infection. However, the role of ER stress manipulation in HBV replication and its underlying mechanisms remain still unclear. Our data showed that mild ER stress inhibited HBV transcription and replication, while severe ER stress enhanced them. Mechanistically, in contrary to the effect on HBV replication, mild ER stress activated whereas severe ER stress inhibited mTOR signaling in HBV-infected cells. Further, mTOR signaling was revealed to be critical for mild ER stress-mediated HBV inhibition. Furthermore, ATF6 but not PERK or IRE1α was found to be involved in mild ER stress-mediated mTOR and the following HBV inhibition. Moreover, ATF6, per se, could inhibit HBV transcription and replication via activating mTOR signaling. Together, ATF6-mediated mild ER stress inhibited HBV transcription and replication through mTOR activation, which might present as an important therapeutic target for CHB patients.

Dengue virus: Etiology, epidemiology, pathobiology, and developments in diagnosis and control - A comprehensive review

Dengue flavivirus (DENV) is the virus that causes dengue, one of the most dangerous and common viral diseases in humans that are carried by mosquitoes and can lead to fatalities. Every year, there are over 400 million cases of dengue fever worldwide, and 22,000 fatalities. It has been documented in tropical and subtropical climates in over 100 nations. Unfortunately, there is no specific treatment approach, but prevention, adequate awareness, diagnosis in the early stages of viral infection and proper medical care can reduce the mortality rate. The first licensed vaccine for dengue virus (CYD Denvaxia) was quadrivalent, but it is not approved in all countries. The primary barriers to vaccine development include inadequate animal models, inadequate etiology mechanistic studies, and adverse drug events. This study provides current knowledge and a comprehensive view of the biology, production and reproduction, transmission, pathogenesis and diagnosis, epidemiology and control measures of dengue virus.

Early host defense against virus infections

Early host defense eliminates many viruses before infections are established while clearing others so they remain subclinical or cause only mild disease. The field of immunology has been shaped by broad concepts, including the pattern recognition theory that currently dominates innate immunology. Focusing on early host responses to virus infections, we analyze the literature to build a working hypothesis for the principles that govern the early line of cellular antiviral defense. Aiming to ultimately arrive at a criteria-based theory with strong explanatory power, we propose that both controlling infection and limiting inflammation are key drivers for the early cellular antiviral response. This response, which we suggest is exerted by a set of "microbe- and inflammation-restricting mechanisms," directly restrict viral replication while also counteracting inflammation. Exploring the mechanisms and physiological importance of the early layer of cellular antiviral defense may open further lines of research in immunology.

Activation of ATF3 via the integrated stress response pathway regulates innate immune response to restrict Zika virus

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus that can have devastating health consequences. The developmental and neurological effects of a ZIKV infection arise in part from the virus triggering cellular stress pathways and perturbing transcriptional programs. To date, the underlying mechanisms of transcriptional control directing viral restriction and virus-host interaction are understudied. Activating Transcription Factor 3 (ATF3) is a stress-induced transcriptional effector that modulates the expression of genes involved in a myriad of cellular processes, including inflammation and antiviral responses, to restore cellular homeostasis. While ATF3 is known to be upregulated during ZIKV infection, the mode by which ATF3 is activated, and the specific role of ATF3 during ZIKV infection is unknown. In this study, we show via inhibitor and RNA interference approaches that ZIKV infection initiates the integrated stress response pathway to activate ATF4 which in turn induces ATF3 expression. Additionally, by using CRISPR-Cas9 system to delete ATF3, we found that ATF3 acts to limit ZIKV gene expression in A549 cells. We also determined that ATF3 enhances the expression of antiviral genes such as STAT1 and other components in the innate immunity pathway to induce an ATF3-dependent anti-ZIKV response. Our study reveals crosstalk between the integrated stress response and innate immune response pathways and highlights an important role for ATF3 in establishing an antiviral effect during ZIKV infection.

IMPORTANCE

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus that co-opts cellular mechanisms to support viral processes that can reprogram the host transcriptional profile. Such viral-directed transcriptional changes and the pro- or anti-viral outcomes remain understudied. We previously showed that ATF3, a stress-induced transcription factor, is significantly upregulated in ZIKV-infected mammalian cells, along with other cellular and immune response genes. We now define the intracellular pathway responsible for ATF3 activation and elucidate the impact of ATF3 expression on ZIKV infection. We show that during ZIKV infection, the integrated stress response pathway stimulates ATF3 which enhances the innate immune response to antagonize ZIKV infection. This study establishes a link between viral-induced stress response and transcriptional regulation of host defense pathways and thus expands our knowledge of virus-mediated transcriptional mechanisms and transcriptional control of interferon-stimulated genes during ZIKV infection.

The roles and mechanisms of endoplasmic reticulum stress-mediated autophagy in animal viral infections

The endoplasmic reticulum (ER) is a unique organelle responsible for protein synthesis and processing, lipid synthesis in eukaryotic cells, and the replication of many animal viruses is closely related to ER. A considerable number of viral proteins are synthesised during viral infection, resulting in the accumulation of unfolded and misfolded proteins in ER, which in turn induces endoplasmic reticulum stress (ERS). ERS further drives three signalling pathways (PERK, IRE1, and ATF6) of the cellular unfolded protein response (UPR) to respond to the ERS. In numerous studies, ERS has been shown to mediate autophagy, a highly conserved cellular degradation mechanism to maintain cellular homeostasis in eukaryotic cells, through the UPR to restore ER homeostasis. ERS-mediated autophagy is closely linked to the occurrence and development of numerous viral diseases in animals. Host cells can inhibit viral replication by regulating ERS-mediated autophagy, restoring the ER's normal physiological process. Conversely, many viruses have evolved strategies to exploit ERS-mediated autophagy to achieve immune escape. These strategies include the regulation of PERK-eIF2α-Beclin1, PERK-eIF2α-ATF4-ATG12, IRE1α-JNK-Beclin1, and other signalling pathways, which provide favourable conditions for the replication of animal viruses in host cells. The ERS-mediated autophagy pathway has become a hot topic in animal virological research. This article reviews the most recent research regarding the regulatory functions of ERS-mediated autophagy pathways in animal viral infections, emphasising the underlying mechanisms in the context of different viral infections. Furthermore, it considers the future direction and challenges in the development of ERS-mediated autophagy targeting strategies for combating animal viral diseases, which will contribute to unveiling their pathogenic mechanism from a new perspective and provide a scientific reference for the discovery and development of new antiviral drugs and preventive strategies.

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.

Exploring the interplay between miRNAs, apoptosis and viral load, in Dengue virus infection

Dengue virus (DENV) is a major global health concern, causing millions of infections annually. Understanding the cellular response to DENV infection is crucial for developing effective therapies. This study provides an in-depth analysis of the cellular response to Dengue virus (DENV) infection, with a specific focus on the interplay between microRNAs (miRNAs), apoptosis, and viral load across different DENV serotypes. Utilizing a variety of cell lines infected with four DENV serotypes, the research methodically quantifies viral load, and the expression levels of miRNA-15, miRNA-16, and BCL2 protein, alongside measuring apoptosis markers. Methodologically, the study employs quantitative PCR for viral load and miRNA expression analysis, and Western blot for apoptosis and BCL2 detection, with a statistical framework that includes ANOVA and correlation analysis to discern significant differences and relationships. The findings reveal that despite similar viral loads across DENV serotypes, DENV-2 exhibits a marginally higher load. A notable upregulation of miRNA-15 and miRNA-16 correlates positively with increased viral load, suggesting their potential role in modulating viral replication. Concurrently, a marked activation of caspases 3 and 7, along with changes in BCL2 protein levels, underscores the role of apoptosis in the cellular response to DENV infection. Conclusively, the study enhances the understanding of miRNA involvement in DENV pathogenesis, highlighting miRNA-15 and miRNA-16 as potential regulatory agents in viral replication and apoptosis. These findings pave the way for further exploration into miRNA-based therapeutic strategies against DENV infection.

Activation of ATF3 via the Integrated Stress Response Pathway Regulates Innate Immune Response to Restrict Zika Virus

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus that can have devastating health consequences. The developmental and neurological effects from a ZIKV infection arise in part from the virus triggering cellular stress pathways and perturbing transcriptional programs. To date, the underlying mechanisms of transcriptional control directing viral restriction and virus-host interaction are understudied. Activating Transcription Factor 3 (ATF3) is a stress-induced transcriptional effector that modulates the expression of genes involved in a myriad of cellular processes, including inflammation and antiviral responses, to restore cellular homeostasis. While ATF3 is known to be upregulated during ZIKV infection, the mode by which ATF3 is activated and the specific role of ATF3 during ZIKV infection is unknown. In this study, we show via inhibitor and RNA interference approaches that ZIKV infection initiates the integrated stress response pathway to activate ATF4 which in turn induces ATF3 expression. Additionally, by using CRISPR-Cas9 system to delete ATF3, we found that ATF3 acts to limit ZIKV gene expression in A549 cells. We also determined that ATF3 enhances the expression of antiviral genes such as STAT1 and other components in the innate immunity pathway to induce an ATF3-dependent anti-ZIKV response. Our study reveals crosstalk between the integrated stress response and innate immune response pathways and highlights an important role for ATF3 in establishing an antiviral effect during ZIKV infection.

Guidelines for the role of autophagy in drug delivery vectors uptake pathways

The process of autophagy refers to the intracellular absorption of cytoplasm (such as proteins, nucleic acids, tiny molecules, complete organelles, and so on) into the lysosome, followed by the breakdown of that cytoplasm. The majority of cellular proteins are degraded by a process called autophagy, which is both a naturally occurring activity and one that may be induced by cellular stress. Autophagy is a system that can save cells' integrity in stressful situations by restoring metabolic basics and getting rid of subcellular junk. This happens as a component of an endurance response. This mechanism may have an effect on disease, in addition to its contribution to the homeostasis of individual cells and tissues as well as the control of development in higher species. The main aim of this study is to discuss the guidelines for the role of autophagy in drug delivery vector uptake pathways. In this paper, we discuss the meaning and concept of autophagy, the mechanism of autophagy, the role of autophagy in drug delivery vectors, autophagy-modulating drugs, nanostructures for delivery systems of autophagy modulators, etc. Later in this paper, we talk about how to deliver chemotherapeutics, siRNA, and autophagy inducers and inhibitors. We also talk about how hard it is to make a drug delivery system that takes nanocarriers' roles as autophagy modulators into account.

Carboplatin restricts peste des petits ruminants virus replication by suppressing the STING-mediated autophagy

Peste des petits ruminants virus (PPRV) is a morbillivirus that causes the acute and highly pathogenic infectious disease peste des petits ruminants (PPR) in small ruminants and poses a major threat to the goat and sheep industries. Currently, there is no effective treatment for PPRV infection. Here, we propose Carboplatin, a platinum-based regimen designed to treat a range of malignancies, as a potential antiviral agent. We showed that Carboplatin exhibits significant antiviral activity against PPRV in a cell culture model. The mechanism of action of Carboplatin against PPRV is mainly attributed to its ability to block STING mediated autophagy. Together, our study supports the discovery of Carboplatin as an antiviral against PPRV and potentially other closely related viruses, sheds light on its mode of action, and establishes STING as a valid and attractive target to counteract viral infection.

SQSTM1 downregulates avian metapneumovirus subgroup C replication via mediating selective autophagic degradation of viral M2-2 protein

Avian metapneumovirus subgroup C (aMPV/C), an important pathogen causing acute respiratory infection in chickens and turkeys, contributes to substantial economic losses in the poultry industry worldwide. aMPV/C has been reported to induce autophagy, which is beneficial to virus replication. Sequestosome 1 (SQSTM1/P62), a selective autophagic receptor, plays a crucial role in viral replication by clearing ubiquitinated proteins. However, the relationship between SQSTM1-mediated selective autophagy and aMPV/C replication is unclear. In this study, we found that the expression of SQSTM1 negatively regulates aMPV/C replication by reducing viral protein expression and viral titers. Further studies revealed that the interaction between SQSTM1 and aMPV/C M2-2 protein is mediated via the Phox and Bem1 (PB1) domain of the former, which recognizes a ubiquitinated lysine at position 67 of the M2-2 protein, and finally degrades M2-2 via SQSTM1-mediated selective autophagy. Collectively, our results reveal that SQSTM1 degrades M2-2 via a process of selective autophagy to suppress aMPV/C replication, thereby providing novel insights for the prevention and control of aMPV/C infection.IMPORTANCEThe selective autophagy plays an important role in virus replication. As an emerging pathogen of avian respiratory virus, clarification of the effect of SQSTM1, a selective autophagic receptor, on aMPV/C replication in host cells enables us to better understand the viral pathogenesis. Previous study showed that aMPV/C infection reduced the SQSTM1 expression accompanied by virus proliferation, but the specific regulatory mechanism between them was still unclear. In this study, we demonstrated for the first time that SQSTM1 recognizes the 67th amino acid of M2-2 protein by the interaction between them, followed by M2-2 degradation via the SQSTM1-mediated selective autophagy, and finally inhibits aMPV/C replication. This information supplies the mechanism by which SQSTM1 negatively regulates viral replication, and provides new insights for preventing and controlling aMPV/C infection.

Plant extracts modulate cellular stress to inhibit replication of mouse Coronavirus MHV-A59

The Covid-19 infection outbreak led to a global epidemic, and although several vaccines have been developed, the appearance of mutations has allowed the virus to evade the immune response. Added to this is the existing risk of the appearance of new emerging viruses. Therefore, it is necessary to explore novel antiviral therapies. Here, we investigate the potential in vitro of plant extracts to modulate cellular stress and inhibit murine hepatitis virus (MHV)-A59 replication. L929 cells were treated with P2Et (Caesalpinia spinosa) and Anamu SC (Petiveria alliacea) plant extracts during infection and virus production, ROS (reactive oxygen species), UPR (unfolded protein response), and autophagy were assessed. P2Et inhibited virus replication and attenuated both ROS production and UPR activation induced during infection. In contrast, the sustained presence of Anamu SC during viral adsorption and replication was required to inhibit viral infection, tending to induce pro-oxidant effects, and increasing UPR gene expression. Notably, the loss of the PERK protein resulted in a slight decrease in virus yield, suggesting a potential involvement of this UPR pathway during replication. Intriguingly, both extracts either maintained or increased the calreticulin surface exposure induced during infection. In conclusion, our findings highlight the development of antiviral natural plant extracts that differentially modulate cellular stress.

An RBM10 and NF-κB interacting host lncRNA promotes JEV replication and neuronal cell death

IMPORTANCE

Central nervous system infection by flaviviruses such as Japanese encephalitis virus, Dengue virus, and West Nile virus results in neuroinflammation and neuronal damage. However, little is known about the role of long non-coding RNAs (lncRNAs) in flavivirus-induced neuroinflammation and neuronal cell death. Here, we characterized the role of a flavivirus-induced lncRNA named JINR1 during the infection of neuronal cells. Depletion of JINR1 during virus infection reduces viral replication and cell death. An increase in GRP78 expression by JINR1 is responsible for promoting virus replication. Flavivirus infection induces the expression of a cellular protein RBM10, which interacts with JINR1. RBM10 and JINR1 promote the proinflammatory transcription factor NF-κB activity, which is detrimental to cell survival.

Seneca Valley Virus Degrades STING via PERK and ATF6-Mediated Reticulophagy

Seneca Valley Virus (SVV), a member of the Picornaviridae family, is an emerging porcine virus that can cause vesicular disease in pigs. However, the immune evasion mechanism of SVV remains unclear, as does its interaction with other pathways. STING (Stimulator of interferon genes) is typically recognized as a critical factor in innate immune responses to DNA virus infection, but its role during SVV infection remains poorly understood. In the present study, we observed that STING was degraded in SVV-infected PK-15 cells, and SVV replication in the cells was affected when STING was knockdown or overexpressed. The STING degradation observed was blocked when the SVV-induced autophagy was inhibited by using autophagy inhibitors (Chloroquine, Bafilomycin A1) or knockdown of autophagy related gene 5 (ATG5), suggesting that SVV-induced autophagy is responsible for STING degradation. Furthermore, the STING degradation was inhibited when reticulophagy regulator 1 (FAM134B), a reticulophagy related receptor, was knocked down, indicating that SVV infection induces STING degradation via reticulophagy. Further study showed that in eukaryotic translation initiation factor 2 alpha kinase 3 (PERK)/activating transcription factor 6 (ATF6) deficient cells, SVV infection failed to induce reticulophagy-medaited STING degradation, indicating that SVV infection caused STING degradation via PERK/ATF6-mediated reticulophagy. Notably, blocking reticulophagy effectively hindered SVV replication. Overall, our study suggested that SVV infection resulted in STING degradation via PERK and ATF6-mediated reticulophagy, which may be an immune escape strategy of SVV. This finding improves the understanding of the intricate interplay between viruses and their hosts and provides a novel strategy for the development of novel antiviral drugs.

Dengue virus NS1 secretion is regulated via importin-subunit β1 controlling expression of the chaperone GRp78 and targeted by the clinical drug ivermectin

IMPORTANCE

Dengue virus (DENV) is a major human pathogen that can cause hemorrhagic fever and shock syndrome. One important factor of DENV pathogenicity is non-structural protein 1 (NS1), a glycoprotein that is secreted from infected cells. Here we study the mode of action of the widely used drug ivermectin, used to treat parasitic infections and recently shown to lower NS1 blood levels in DENV-infected patients. We found that ivermectin blocks the nuclear transport of transcription factors required for the expression of chaperones that support the folding and secretion of glycoproteins, including NS1. Impairing nuclear transport of these transcription factors by ivermectin or depleting them from infected cells dampens NS1 folding and thus its secretion. These results reveal a novel mode of action of ivermectin that might apply to other flaviviruses as well.

Dengue virus 3 genotype I (GI) lineage 1 (L1) isolates elicit differential cytopathic effect with syncytium formation in human glioblastoma cells (U251)

BACKGROUND

Dengue virus (DENV) is a Flaviviridae member classified into four antigenically distinct serotypes (DENV 1, 2, 3, and 4) and further subdivided genotypes. DENV3 is subdivided into four or five genotypes, depending on the classification adopted. Despite their high genetic proximity, as revealed by phylogenetic complete polyprotein analysis, DENV3 MG-20 and DENV3 PV_BR showed different neurovirulence in mice models. Our group identified six amino acid mutations in protein E, including the E62K and E123Q, which may affect interactions of hydrophobic clusters on domain II, thus leading to the observed differences in the studied viruses.

METHODS

Human glioblastoma cells (U251) derived from a malignant glioblastoma tumor by explant technique were infected by the DENV3 GIL1 isolates DENV3 MG-20 and DENV3 PV_BR and analyzed by plaque assays and titration, optical, immunofluorescence, and transmission electronic microscopy.

RESULTS

The two isolates showed different cytopathic effects (CPE) and fusogenic patterns, further confirmed by indirect immunofluorescence. Transmission electron microscopy revealed intense cytopathic effects in DENV3 MG-20 infected U251 cells, displaying endoplasmic reticulum hypertrophy and turgid vesicles with proteins and multiple viruses, distinct from DENV3 PV_BR infected cells. It is hypothesized that the different amino acids in the DENV3 MG-20 isolate are related to an increased membrane fusion ability in viral infection, thus facilitating immune system evasion and increased chances of central nervous system cell infection.

CONCLUSION

These results emphasize the biological differences between the isolates, which could be a critical factor in host-virus interaction and severe dengue development. Our study presents comparative results of highly similar isolates with the potential to generate more subsidies for a deeper understanding of the DENV pathogenesis. The neurotropism of the isolate DENV3 MG-20 (belonging to the DENV3 GI L1 genotype) showing infection of nervous system cells (U251) could contribute to understanding neurological dengue disease.

Super-resolution proximity labeling reveals anti-viral protein network and its structural changes against SARS-CoV-2 viral proteins

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replicates in human cells by interacting with host factors following infection. To understand the virus and host interactome proximity, we introduce a super-resolution proximity labeling (SR-PL) method with a "plug-and-playable" PL enzyme, TurboID-GBP (GFP-binding nanobody protein), and we apply it for interactome mapping of SARS-CoV-2 ORF3a and membrane protein (M), which generates highly perturbed endoplasmic reticulum (ER) structures. Through SR-PL analysis of the biotinylated interactome, 224 and 272 peptides are robustly identified as ORF3a and M interactomes, respectively. Within the ORF3a interactome, RNF5 co-localizes with ORF3a and generates ubiquitin modifications of ORF3a that can be involved in protein degradation. We also observe that the SARS-CoV-2 infection rate is efficiently reduced by the overexpression of RNF5 in host cells. The interactome data obtained using the SR-PL method are presented at https://sarscov2.spatiomics.org. We hope that our method will contribute to revealing virus-host interactions of other viruses in an efficient manner.

NLRC5 restricts dengue virus infection by promoting the autophagic degradation of viral NS3 through E3 ligase CUL2 (cullin 2)

NLRC5 has been reported to be involved in antiviral immunity; however, the underlying mechanism remains poorly understood. Here, we investigated the functional role of NLRC5 in the infection of a flavivirus, dengue virus (DENV). We found that the expression of NLRC5 was strongly induced by virus infection and IFNB or IFNG stimulation in different cell lines. Overexpression of NLRC5 remarkably suppressed DENV infection, whereas knockout of NLRC5 led to a significant increase in DENV infection. Mechanistic study revealed that NLRC5 interacted with the viral nonstructural protein 3 (NS3) protease domain and mediated degradation of NS3 through a ubiquitin-dependent selective macroautophagy/autophagy pathway. We demonstrated that NLRC5 recruited the E3 ubiquitin ligase CUL2 (cullin 2) to catalyze K48-linked poly-ubiquitination of the NS3 protease domain, which subsequently served as a recognition signal for cargo receptor TOLLIP-mediated selective autophagic degradation. Together, we have demonstrated that NLRC5 exerted an antiviral effect by mediating the degradation of a multifunctional protein of DENV, providing a novel antiviral signal axis of NLRC5-CUL2-NS3-TOLLIP. This study expands our understanding of the regulatory network of NLRC5 in the host defense against virus infection.

The chaperone BiP promotes dengue virus replication and mosquito vitellogenesis in Aedes aegypti

Binding immunoglobulin protein (BiP, also known as GRP78), a chaperone and master regulator of the unfolded protein response (UPR) pathway, plays an essential role in several flavivirus infections, but its functional role in regulating dengue virus replication in the mosquito remains largely unknown. We here demonstrated the interaction between a dengue virus serotype 2 (DENV2) and BiP in Aedes aegypti and report the discovery of a novel functional role of BiP in mosquito vitellogenesis. Silencing Ae. aegypti BiP (AaBiP) expression resulted in the significant inhibition of DENV2 viral genome replication, viral protein production, and infectious viral particle biogenesis. Co-immunoprecipitation assays showed that the DENV2 non-structural protein 1 (NS1) interacts with the AaBiP protein, and silencing AaBiP expression led to enhanced DENV2 NS1 aggregation, indicating that AaBiP plays a role in viral protein stability. A kinetic study focusing on pulse treatment of MG132, a proteasome inhibitor, in AaBiP-silenced mosquitoes showed that DENV2 NS1 was drastically elevated, which further suggests that AaBiP-mediated viral protein degradation is mediated by proteasomal machinery. Silencing of AaBiP also resulted in a reduction in mosquito fertility and fecundity. Depletion of AaBiP inhibited mosquito vitellogenesis due to the reduction of vitellogenin mRNA and elevated aggregation of vitellogenin protein post blood meal, further suppressing ovary development and fecundity. Overall, our results suggest that AaBiP is a dual-function protein with roles in both the regulation of dengue virus replication and mosquito reproduction. Our findings will be useful in the establishment of more efficient strategies for vector-borne disease control.

Crosstalk Between Autophagy and Inflammation in Chronic Cerebral Ischaemia

Chronic cerebral ischaemia (CCI) is a high-incidence cardiovascular and cerebrovascular disease that is very common in clinical practice. Although many pathogenic mechanisms have been explored, there is still great controversy among neuroscientists regarding the pathogenesis of CCI. Therefore, it is important to elucidate the mechanisms of CCI occurrence and progression for the prevention and treatment of ischaemic cerebrovascular disorders. Autophagy and inflammation play vital roles in CCI, but the relationship between these two processes in this disease remains unknown. Here, we review the progression and discuss the functions, actions and pathways of autophagy and inflammation in CCI, including a comprehensive view of the transition from acute disease to CCI through ischaemic repair mechanisms. This review may provide a reference for future research and treatment of CCI. Schematic diagram of the interplay between autophagy and inflammation in CCI. CCI lead to serious, life-threatening complications. This review summarizes two factors in CCI, including autophagy and inflammation, which have been focused for the mechanisms of CCI. In short, the possible points of intersection are shown in the illustration. CCI, Chronic cerebral ischaemia; ER stress, Endoplasmic reticulum stress; ROS, Reactive oxygen species.

4-Phenyl-butyric Acid Inhibits Japanese Encephalitis Virus Replication via Inhibiting Endoplasmic Reticulum Stress Response

Japanese encephalitis virus (JEV) infection causes host endoplasmic reticulum stress (ERS) reaction, and then induces cell apoptosis through the UPR pathway, invading the central nervous system and causing an inflammation storm. The endoplasmic reticulum stress inhibitor, 4-phenyl-butyric acid (4-PBA), has an inhibitory effect on the replication of flavivirus. Here, we studied the effect of 4-PBA on JEV infection both in vitro and vivo. The results showed that 4-PBA treatment could significantly decrease the titer of JEV, inhibit the expression of the JEV NS3 protein (in vitro, p < 0.01) and reduce the positive rate of the JEV E protein (in vivo, p < 0.001). Compared to the control group, 4-PBA treatment can restore the weight of JEV-infected mice, decrease the level of IL-1β in serum and alleviate the abnormalities in brain tissue structure. Endoplasmic reticulum stress test found that the expression level of GRP78 was much lower and activation levels of PERK and IRE1 pathways were reduced in the 4-PBA treatment group. Furthermore, 4-PBA inhibited the UPR pathway activated by NS3, NS4b and NS5 RdRp. The above results indicated that 4-PBA could block JEV replication and inhibit ER stress caused by JEV. Interestingly, 4-PBA could reduce the expression of NS5 by inhibiting transcription (p < 0.001), but had no effect on the expression of NS3 and NS4b. This result may indicate that 4-PBA has antiviral activity independent of the UPR pathway. In summary, the effect of 4-PBA on JEV infection is related to the inhibition of ER stress, and it may be a promising drug for the treatment of Japanese encephalitis.

Vitamin D Deficiency (VDD) and Susceptibility towards Severe Dengue Fever-A Prospective Cross-Sectional Study of Hospitalized Dengue Fever Patients from Lahore, Pakistan

Dengue is a mosquito-borne flaviviral serious febrile illness, most common in the tropical and subtropical regions including Pakistan. Vitamin D is a strong immunomodulator affecting both the innate and adaptive immune responses and plays a pivotal role in pathogen-defense mechanisms. There has been considerable interest in the possible role of vitamin D in dengue viral (DENV) infection. In the present prospective cross-sectional study, we assessed a possible association between serum vitamin D deficiency (VDD) and susceptibility towards severe dengue fever (DF) illness. Serum vitamin D levels were measured at the time of hospitalization in 97 patients diagnosed with dengue fever (DF), dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS) at Mayo Hospital, King Edward Medical University, Lahore, PK, from 16 November 2021 to 15 January 2022. In terms of disease severity, 37 (38.1%) patients were DF, 52 (53.6%) were DHF grade 1 and 2, and 8 (8.2%) were DSS. The results revealed that most patients (75 (77.3%)) were vitamin-D-deficient (i.e., serum level < 20 ng/mL), including 27 (73.0%) in DF, 41 (78.8%) in DHF grade 1 and 2, and 7 (87.5%) in DSS. The degree of VDD was somewhat higher in DSS patients as compared to DF and DHF grade 1 and 2 patients. Overall, serum vitamin D levels ranged from 4.2 to 109.7 ng/mL, and the median (IQR) was in the VDD range, i.e., 12.2 (9.1, 17.8) ng/mL. Our results suggest that there may be a possible association between VDD and susceptibility towards severe dengue illness. Hence, maintaining sufficient vitamin D levels in the body either through diet or supplementation may help provide adequate immune protection against severe dengue fever illness. Further research is warranted.

Defective Mitochondrial Quality Control during Dengue Infection Contributes to Disease Pathogenesis

Mitochondrial fitness is governed by mitochondrial quality control pathways comprising mitochondrial dynamics and mitochondrial-selective autophagy (mitophagy). Disruption of these processes has been implicated in many human diseases, including viral infections. Here, we report a comprehensive analysis of the effect of dengue infection on host mitochondrial homeostasis and its significance in dengue disease pathogenesis. Despite severe mitochondrial stress and injury, we observed that the pathways of mitochondrial quality control and mitochondrial biogenesis are paradoxically downregulated in dengue-infected human liver cells. This leads to the disruption of mitochondrial homeostasis and the onset of cellular injury and necrotic death in the infected cells. Interestingly, dengue promotes global autophagy but selectively disrupts mitochondrial-selective autophagy (mitophagy). Dengue downregulates the expression of PINK1 and Parkin, the two major proteins involved in tagging the damaged mitochondria for elimination through mitophagy. Mitophagy flux assays also suggest that Parkin-independent pathways of mitophagy are also inactive during dengue infection. Dengue infection also disrupts mitochondrial biogenesis by downregulating the master regulators PPARγ and PGC1α. Dengue-infected cells release mitochondrial damage-associated molecular patterns (mtDAMPs) such as mitochondrial DNA into the cytosol and extracellular milieu. Furthermore, the challenge of naive immune cells with culture supernatants from dengue-infected liver cells was sufficient to trigger proinflammatory signaling. In correlation with our in vitro observations, dengue patients have high levels of cell-free mitochondrial DNA in their blood in proportion to the degree of thrombocytopenia. Overall, our study shows how defective mitochondrial homeostasis in dengue-infected liver cells can drive dengue disease pathogenesis. IMPORTANCE Many viruses target host cell mitochondria to create a microenvironment conducive to viral dissemination. Dengue virus also exploits host cell mitochondria to facilitate its viral life cycle. Dengue infection of liver cells leads to severe mitochondrial injury and inhibition of proteins that regulate mitochondrial quality control and biogenesis, thereby disrupting mitochondrial homeostasis. A defect in mitochondrial quality control leads to the accumulation of damaged mitochondria and promotes cellular injury. This leads to the release of mitochondrial damage-associated molecular patterns (mt-DAMPs) into the cell cytoplasm and extracellular milieu. These mt-DAMPs activate the naive immune cells and trigger proinflammatory signaling, leading to the release of cytokines and chemokines, which may trigger systemic inflammation and contribute to dengue disease pathogenesis. In correlation with this, we observed high levels of cell-free mitochondrial DNA in dengue patient blood. This study provides insight into how the disruption of mitochondrial quality control in dengue-infected cells can trigger inflammation and drive dengue disease pathogenesis.

The Involvement of Atlastin in Dengue Virus and Wolbachia Infection in Aedes aegypti and Its Regulation by aae-miR-989

Endoplasmic reticulum (ER)-shaping atlastin proteins (ATLs) have been demonstrated to play a functional role during flavivirus replication in mammalian cells. For dengue virus (DENV), atlastin is required in the formation of the replication organelles and RNA replication, virion assembly, production of the infectious virus particles, and trafficking or directing the association of vesicle packets with furin. Here, we investigated the involvement of atlastin in DENV replication in the mosquito Aedes aegypti and explored the possibility of its manipulation by the endosymbiotic bacterium Wolbachia to interfere with DENV replication. Results showed the expression of Ae. aegypti atlastin gene (AaATL) was upregulated in DENV-infected Aag2 cells, and its silencing led to reduced DENV replication. Contrary to our assumption that AaATL could be downregulated by Wolbachia, we did not find evidence for that in Wolbachia-infected cell lines, but this was the case in mosquitoes. Further, silencing AaATL did not have any effect on Wolbachia density. Our results also suggest that aae-miR-989 miRNA negatively regulates AaATL. The oversupply of the miRNA mimic led to reduced DENV replication consistent with the positive role of AaATL in DENV replication. Overall, the results favor AaATL's involvement in DENV replication; however, there is no support that the protein is involved in Wolbachia-mediated DENV inhibition. In addition, the results contribute to discerning further possible overlapping functions of ATLs in mosquitoes and mammalian cells. IMPORTANCE Atlastin is a protein associated with the endoplasmic reticulum and has been shown to play a role in replication of flaviviruses in mammalian cells. This study aimed to investigate the role of mosquito Aedes aegypti atlastin (AaATL) in dengue virus replication and maintenance of Wolbachia, an endosymbiotic bacterium, in the mosquito. Our results suggest that AaATL facilitates dengue virus replication in mosquito cells, considering silencing the gene led to reductions in virus replication and virion production. Further, AaATL was found to be regulated by a mosquito microRNA, aae-miR-989. Despite an effect on dengue virus, AaATL silencing did not affect Wolbachia replication and maintenance in mosquito cells. The results shed light on the role of atlastins in mosquito-pathogen interactions and their overlapping roles in mosquito and mammalian cells.

Endoplasmic Stress Affects the Coinfection of Leishmania Amazonensis and the Phlebovirus (Bunyaviridae) Icoaraci

Viral coinfections can modulate the severity of parasitic diseases, such as human cutaneous leishmaniasis. Leishmania parasites infect thousands of people worldwide and cause from single cutaneous self-healing lesions to massive mucosal destructive lesions. The transmission to vertebrates requires the bite of Phlebotomine sandflies, which can also transmit Phlebovirus. We have demonstrated that Leishmania infection requires and triggers the Endoplasmic stress (ER stress) response in infected macrophages. In the present paper, we tested the hypothesis that ER stress is increased and required for the aggravation of Leishmania infection due to coinfection with Phlebovirus. We demonstrated that Phlebovirus Icoaraci induces the ER stress program in macrophages mediated by the branches IRE/XBP1 and PERK/ATF4. The coinfection with L. amazonensis potentiates and sustains the ER stress, and the inhibition of IRE1α or PERK results in poor viral replication and decreased parasite load in macrophages. Importantly, we observed an increase in viral replication during the coinfection with Leishmania. Our results demonstrated the role of ER stress branches IRE1/XBP1 and PERK/ATF4 in the synergic effect on the Leishmania increased load during Phlebovirus coinfection and suggests that Leishmania infection can also increase the replication of Phlebovirus in macrophages.

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.

Peste des petits ruminants virus induces ERS-mediated autophagy to promote virus replication

Peste des petits ruminants virus (PPRV) has long been a significant threat to small ruminant productivity worldwide. Virus infection-induced endoplasmic reticulum (ER) stress (ERS) and the subsequently activated unfolded protein response (UPR) play significant roles in viral replication and pathogenesis. However, the relationship between ERS and PPRV infection is unknown. In this study, we demonstrated that ERS was induced during PPRV infection in caprine endometrial epithelial cells (EECs). Importantly, we demonstrated that the induction of autophagy by PPRV was mediated by ERS. Furthermore, we found that the PERK/eIF2α pathway but not the ATF6 or IRE1 pathway was activated and that the activated PERK/eIF2α pathway participated in regulating ERS-mediated autophagy. Moreover, virus replication was required for PPRV infection-induced ERS-mediated autophagy and PERK pathway activation. Additionally, we revealed that either the viral nucleocapsid (N) or nonstructural protein C was sufficient to elicit ERS and activate the PERK/eIF2α pathway, which further increased autophagy. Taken together, these results suggest that PPRV N and C protein-induced autophagy enhances viral replication through the induction of ERS and that the PERK pathway may be involved in the activation of ERS-mediated autophagy during PPRV infection.

Induction and modulation of the unfolded protein response during porcine deltacoronavirus infection

Porcine deltacoronavirus (PDCoV) is an emerging enteropathogenic coronavirus that has the potential for cross-species infection. Many viruses have been reported to induce endoplasmic reticulum stress (ERS) and activate the unfolded protein response (UPR). To date, little is known about whether and, if so, how the UPR is activated by PDCoV infection. Here, we investigated the activation state of UPR pathways and their effects on viral replication during PDCoV infection. We found that PDCoV infection induced ERS and activated all three known UPR pathways (inositol-requiring enzyme 1 [IRE1], activating transcription factor 6 [ATF6], and PKR-like ER kinase [PERK]), as demonstrated by IRE1-mediated XBP1 mRNA cleavage and increased mRNA expression of XBP1s, ATF4, CHOP, GADD34, GRP78, and GRP94, as well as phosphorylated eIF2α expression. Through pharmacologic treatment, RNA interference, and overexpression experiments, we confirmed the negative role of the PERK-eIF2α pathway and the positive regulatory role of the ATF6 pathway, but found no obvious effect of IRE1 pathway, on PDCoV replication. Taken together, our results characterize, for the first time, the state of the ERS response during PDCoV infection and identify the PERK and ATF6 pathways as potential antiviral targets.

DDIT3 antagonizes innate immune response to promote bovine alphaherpesvirus 1 replication via the DDIT3-SQSTM1-STING pathway

DNA damage-inducible transcript 3 (DDIT3), a transcription factor, is typically involved in virus replication control. We are the first to report that DDIT3 promotes the replication of bovine viral diarrhea virus, an RNA virus, by inhibiting innate immunity. However, whether the DDIT3 gene participates in DNA virus replication by regulating innate immunity remains unclear. This study reported that DDIT3 suppressed the innate immune response caused by DNA viruses to promote bovine herpesvirus 1 (BoHV-1) replication. After BoHV-1 infection of Madin-Darby bovine kidney (MDBK) cells, upregulated expression of DDIT3 induced SQSTM1-mediated autophagy and promoted STING degradation. Overexpression of the SQSTM1 protein effectively reduced STING protein levels, whereas SQSTM1 knockdown increased STING protein levels. Coimmunoprecipitation experiments and confocal laser scanning microscopy revealed that the SQSTM1 protein interacts with and colocalizes with STING. Knockdown of SQSTM1 expression in DDIT3-overexpressing cell lines restored STING protein levels. Moreover, a dual-luciferase reporter assay revealed that DDIT3 directly binds to the bovine SQSTM1 promoter and induces SQSTM1 transcription. Overexpression of SQSTM1 promoted BoHV-1 replication by inhibiting IFN-β and IFN-stimulated genes (ISGs) production; silencing of SQSTM1 promoted the expression of IFN-β and ISGs to inhibit BoHV-1 replication. In conclusion, DDIT3 targets STING via SQSTM1-mediated autophagy to promote BoHV-1 replication. These results suggest a novel mechanism by which DDIT3 regulates DNA virus replication by targeting innate immunity. DDIT3 antagonizes the innate immune response to promote bovine alphaherpesvirus 1 replication via the DDIT3-SQSTM1-STING pathway.

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.

The Regulation of Integrated Stress Response Signaling Pathway on Viral Infection and Viral Antagonism

The integrated stress response (ISR) is an adaptational signaling pathway induced in response to different stimuli, such as accumulation of unfolded and misfolded proteins, hypoxia, amino acid deprivation, viral infection, and ultraviolet light. It has been known that viral infection can activate the ISR, but the role of the ISR during viral infection is still unclear. In some cases, the ISR is a protective mechanism of host cells against viral infection, while viruses may hijack the ISR for facilitating their replication. This review highlighted recent advances on the induction of the ISR upon viral infection and the downstream responses, such as autophagy, apoptosis, formation of stress granules, and innate immunity response. We then discussed the molecular mechanism of the ISR regulating viral replication and how viruses antagonize this cellular stress response resulting from the ISR.

Autophagy inhibitors alleviate Japanese encephalitis virus-induced cerebral inflammation in mice

Japanese encephalitis (JE) is a zoonotic epidemic disease caused by Japanese encephalitis virus (JEV), and currently, no medicines are available to treat this disease. Autophagy modulators play an important role in the treatment of tumors, heart disease, and some viral diseases. The aim of this study was to investigate the effects of autophagy modulators on JEV infection and the host response in mice. The experimental mice were grouped as follows: DMEM (control), JEV, JEV+rapamycin (JEV+Rapa), JEV+wortmannin (JEV+Wort), JEV+chloroquine (JEV+CQ), Rapa, Wort, and CQ. The control group was treated with DMEM. The mice in other groups were infected with 10⁵ PFU of JEV, and Rapa, Wort, and CQ were administered 2 h prior to JEV challenge and then administered daily for 10 consecutive days. All mice were monitored for neurological signs and survival. The damage of subcellular structures in the mouse brain was evaluated by transmission electron microscopy. The distribution of virus in the mouse brain was determined by RNAScope staining and immunohistochemical staining. The neuroinflammatory responses in the brain were examined via quantitative real-time PCR, and the signal pathways involved in neuroinflammation were identified by Western blot. The mice in the JEV+Wort and JEV+CQ groups showed milder neurological symptoms, less damage to the mitochondria in the brain tissue, and a higher survival rate than those in the JEV+Rapa and JEV groups. Compared with the JEV+Rapa and JEV groups, the distribution of JEV in the brain of mice in the JEV+Wort and JEV+CQ groups was lower, and the inflammatory response was weaker. No significant difference was observed in the expression of the PI3K/AKT/NF-κB pathway in mouse brain among the different groups. Our study suggests that the autophagy inhibitors Wort and CQ reduce JEV infection and weaken the inflammatory response, which does not depend on the PI3K/AKT/NF-κB pathway in mouse brain.

Replication of Dengue Virus in K562-Megakaryocytes Induces Suppression in the Accumulation of Reactive Oxygen Species

Dengue virus can infect human megakaryocytes leading to decreased platelet biogenesis. In this article, we report a study of Dengue replication in human K562 cells undergoing PMA-induced differentiation into megakaryocytes. PMA-induced differentiation in these cells recapitulates steps of megakaryopoiesis including gene activation, expression of CD41/61 and CD61 platelet surface markers and accumulation of intracellular reactive oxygen species (ROS). Our results show differentiating megakaryocyte cells to support higher viral replication without any apparent increase in virus entry. Further, Dengue replication suppresses the accumulation of ROS in differentiating cells, probably by only augmenting the activity of the transcription factor NFE2L2 without influencing the expression of the coding gene. Interestingly pharmacological modulation of NFE2L2 activity showed a simultaneous but opposite effect on intracellular ROS and virus replication suggesting the former to have an inhibitory effect on the later. Also cells that differentiated while supporting intracellular virus replication showed reduced level of surface markers compared to uninfected differentiated cells.

RNA-Binding Proteins as Regulators of Internal Initiation of Viral mRNA Translation

Viruses are obligate intracellular parasites that depend on the host’s protein synthesis machinery for translating their mRNAs. The viral mRNA (vRNA) competes with the host mRNA to recruit the translational machinery, including ribosomes, tRNAs, and the limited eukaryotic translation initiation factor (eIFs) pool. Many viruses utilize non-canonical strategies such as targeting host eIFs and RNA elements known as internal ribosome entry sites (IRESs) to reprogram cellular gene expression, ensuring preferential translation of vRNAs. In this review, we discuss vRNA IRES-mediated translation initiation, highlighting the role of RNA-binding proteins (RBPs), other than the canonical translation initiation factors, in regulating their activity.

In human astrocytes neurotropic flaviviruses increase autophagy, yet their replication is autophagy-independent

Astrocytes, an abundant type of glial cells, are the key cells providing homeostasis in the central nervous system. Due to their susceptibility to infection, combined with high resilience to virus-induced cell death, astrocytes are now considered one of the principal types of cells, responsible for virus retention and dissemination within the brain. Autophagy plays an important role in elimination of intracellular components and in maintaining cellular homeostasis and is also intertwined with the life cycle of viruses. The physiological significance of autophagy in astrocytes, in connection with the life cycle and transmission of viruses, remains poorly investigated. In the present study, we investigated flavivirus-induced modulation of autophagy in human astrocytes by monitoring a tandem fluorescent-tagged LC3 probe (mRFP-EGFP-LC3) with confocal and super-resolution fluorescence microscopy. Astrocytes were infected with tick-borne encephalitis virus (TBEV) or West Nile virus (WNV), both pathogenic flaviviruses, and with mosquito-only flavivirus (MOF), which is considered non-pathogenic. The results revealed that human astrocytes are susceptible to infection with TBEV, WNV and to a much lower extent also to MOF. Infection and replication rates of TBEV and WNV are paralleled by increased rate of autophagy, whereas autophagosome maturation and the size of autophagic compartments are not affected. Modulation of autophagy by rapamycin and wortmannin does not influence TBEV and WNV replication rate, whereas bafilomycin A1 attenuates their replication and infectivity. In human astrocytes infected with MOF, the low infectivity and the lack of efficient replication of this flavivirus are mirrored by the absence of an autophagic response.

Flavivirus infections induce a Golgi stress response in vertebrate and mosquito cells

The stress of the Golgi apparatus is an autoregulatory mechanism that is induced to compensate for greater demand in the Golgi functions. No examples of Golgi stress responses due to physiological stimuli are known. Furthermore, the impact on this organelle of viral infections that occupy the vesicular transport during replication is unknown. In this work, we evaluated if a Golgi stress response is triggered during dengue and Zika viruses replication, two flaviviruses whose replicative cycle is heavily involved with the Golgi complex, in vertebrate and mosquito cells. Using GM-130 as a Golgi marker, and treatment with monensin as a positive control for the induction of the Golgi stress response, a significant expansion of the Golgi cisternae was observed in BHK-21, Vero E6 and mosquito cells infected with either virus. Activation of the TFE3 pathway was observed in the infected cells as indicated by the translocation from the cytoplasm to the nucleus of TFE3 and increased expression of pathway targeted genes. Of note, no sign of activation of the stress response was observed in CRFK cells infected with Feline Calicivirus (FCV), a virus released by cell lysis, not requiring vesicular transport. Finally, dilatation of the Golgi complex and translocation of TFE3 was observed in vertebrate cells expressing dengue and Zika viruses NS1, but not NS3. These results indicated that infections by dengue and Zika viruses induce a Golgi stress response in vertebrate and mosquito cells due to the increased demand on the Golgi complex imposed by virion and NS1 processing and secretion.

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.

The Autophagosomes Containing Dengue Virus Proteins and Full-Length Genomic RNA Are Infectious

Autophagic machinery is involved in selective and non-selective recruitment as well as degradation or exocytosis of cargoes, including pathogens. Dengue virus (DENV) infection induces autophagy that enhances virus replication and vesicle release to evade immune system surveillance. This study reveals that DENV2 induces autophagy in lung and liver cancer cells and showed that DENV2 capsid, envelope, NS1, NS3, NS4B and host cell proinflammatory high mobility group box 1 (HMGB1) proteins associated with autophagosomes which were purified by gradient centrifugation. Capsid, NS1 and NS3 proteins showing high colocalization with LC3 protein in the cytoplasm of the infected cells were detected in the purified double-membrane autophagosome by immunogold labeling under transmission electron microscopy. In DENV infected cells, the levels of capsid, envelope, NS1 and HMGB1 proteins are not significantly changed compared to the dramatic accumulation of LC3-II and p62/SQSTM1 proteins when autophagic degradation was blocked by chloroquine, indicating that these proteins are not regulated by autophagic degradation machinery. We further demonstrated that purified autophagosomes were infectious when co-cultured with uninfected cells. Notably, these infectious autophagosomes contain DENV2 proteins, negative-strand and full-length genomic RNAs, but no viral particles. It is possible that the infectivity of the autophagosome originates from the full-length DENV RNA. Moreover, we reveal that DENV2 promotes HMGB1 exocytosis partially through secretory autophagy. In conclusion, we are the first to report that DENV2-induced double-membrane autophagosomes containing viral proteins and full-length RNAs are infectious and not undergoing autophagic degradation. Our novel finding warrants further validation of whether these intracellular vesicles undergo exocytosis to become infectious autophagic vesicles.

Computational analysis of human host binding partners of chikungunya and dengue viruses during coinfection

Mosquito-borne viral diseases like chikungunya and dengue infections can cause severe illness and have become major public health concerns. Chikungunya virus (CHIKV) and dengue virus (DENV) infections share similar primary clinical manifestations and are transmitted by the same vector. Thus, the probability of their coinfection gets increased with more severe clinical complications in the patients. The present study was undertaken to elucidate the common human interacting partners of CHIKV and DENV proteins during coinfection. The viral-host protein-protein interactome was constructed using Cytoscape. Subsequently, significant host interactors were identified during coinfection. The network analysis elucidated 57 human proteins interacting with both CHIKV and DENV, represented as hub-bottlenecks. The functional and biological analyses of the 40 hub-bottlenecks revealed that they are associated with phosphoinositide 3-kinases (PI3K)/AKT, p53 signaling pathways, regulation of cell cycle and apoptosis during coinfection. Moreover, the molecular docking analysis uncovered the tight and robust binding of selected hub-bottlenecks with CHIKV/DENV proteins. Additionally, 23 hub-bottlenecks were predicted as druggable candidates that could be targeted to eradicate the host-viral interactions. The elucidated common host binding partners during DENV and CHIKV coinfection as well as indicated approved drugs can support the therapeutics development.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

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.

Regulation of innate immune signaling pathways by autophagy in dengue virus infection

Autophagy is not only an intracellular recycling degradation system that maintains cellular homeostasis but is also a component of innate immunity that contributes to host defense against viral infection. The viral components as well as viral particles trapped in autophagosomes can be delivered to lysosomes for degradation. Abundant evidence indicates that dengue virus (DENV) has evolved the potent ability to hijack or subvert autophagy process for escaping host immunity and promoting viral replication. Moreover, autophagy is often required to deliver viral components to pattern recognition receptors signaling for interferon (IFN)-mediated viral elimination. Hence, this review summarizes DENV-induced autophagy, which exhibits dual effects on proviral activity of promoting replication and antiviral activity to eliminating viral particles.

Sec62 Regulates Endoplasmic Reticulum Stress and Autophagy Balance to Affect Foot-and-Mouth Disease Virus Replication

Endoplasmic reticulum (ER) stress-induced autophagy is closely associated with viral infection and propagation. However, the intrinsic link between ER stress, autophagy, and viral replication during foot-and-mouth disease virus (FMDV) infection is not fully elucidated. Our previous studies demonstrated that FMDV infection activated the ER stress-associated UPR of the PERK-eIF2a and ATF6 signaling pathway, whereas the IRE1a signaling was suppressed. We found that the activated-ATF6 pathway participated in FMDV-induced autophagy and FMDV replication, while the IRE1α pathway only affected FMDV replication. Further studies indicated that Sec62 was greatly reduced in the later stages of FMDV infection and blocked the activation of the autophagy-related IRE1α-JNK pathway. Moreover, it was also found that Sec62 promoted IRE1a phosphorylation and negatively regulated FMDV proliferation. Importantly, Sec62 may interact with LC3 to regulate ER stress and autophagy balance and eventually contribute to FMDV clearance via fusing with lysosomes. Altogether, these results suggest that Sec62 is a critical molecule in maintaining and recovering ER homeostasis by activating the IRE1α-JNK pathway and delivering autophagosome into the lysosome, thus providing new insights on FMDV-host interactions and novel antiviral therapies.

The endoplasmic reticulum unfolded protein response - homeostasis, cell death and evolution in virus infections

Viruses elicit cell and organismic stress, and offset homeostasis. They trigger intrinsic, innate and adaptive immune responses, which limit infection. Viruses restore homeostasis by harnessing evolutionary conserved stress responses, such as the endoplasmic reticulum (ER) unfolded protein response (UPRER). The canonical UPRER restores homeostasis based on a cell-autonomous signalling network modulating transcriptional and translational output. The UPRER remedies cell damage, but upon severe and chronic stress leads to cell death. Signals from the UPRER flow along three branches with distinct stress sensors, the inositol requiring enzyme (Ire) 1, protein kinase R (PKR)-like ER kinase (PERK), and the activating transcription factor 6 (ATF6). This review shows how both enveloped and non-enveloped viruses use the UPRER to control cell stress and metabolic pathways, and thereby enhance infection and progeny formation, or undergo cell death. We highlight how the Ire1 axis bypasses apoptosis, boosts viral transcription and maintains dormant viral genomes during latency and persistence periods concurrent with long term survival of infected cells. These considerations open new options for oncolytic virus therapies against cancer cells where the UPRER is frequently upregulated. We conclude with a discussion of the evolutionary impact that viruses, in particular retroviruses, and anti-viral defense has on the UPRER.

Specific Interaction of DDX6 with an RNA Hairpin in the 3' UTR of the Dengue Virus Genome Mediates G1 Phase Arrest

The extent to which viral genomic RNAs interact with host factors and contribute to host response and disease pathogenesis is not well known. Here, we report that the human RNA helicase DDX6 specifically binds to the viral most conserved RNA hairpin in the A3 element in the dengue 3' UTR, with nanomolar affinities. DDX6 CLIP confirmed the interaction in HuH-7 cells infected by dengue virus serotype 2. This interaction requires three conserved residues-Lys³⁰⁷, Lys³⁶⁷, and Arg³⁶⁹-as well as the unstructured extension in the C-terminal domain of DDX6. Interestingly, alanine substitution of these three basic residues resulted in RNA-independent ATPase activity, suggesting a mechanism by which RNA-binding and ATPase activities are coupled in DEAD box helicases. Furthermore, we applied a cross-omics gene enrichment approach to suggest that DDX6 is functionally related to cell cycle regulation and viral pathogenicity. Indeed, infected cells exhibited cell cycle arrest in G₁ phase and a decrease in the early S phase. Exogenous expression of intact DDX6, but not A3-binding-deficient mutants, alleviated these effects by rescue of the DNA preinitiation complex expression. Disruption of the DDX6-binding site was found in dengue and Zika live-attenuated vaccine strains. Our results suggested that dengue virus has evolved an RNA aptamer against DDX6 to alter host cell states and defined DDX6 as a new regulator of G₁/S transition. IMPORTANCE Dengue virus (DENV) is transmitted by mosquitoes to humans, infecting 390 million individuals per year globally. About 20% of infected patients shows a spectrum of clinical manifestation, ranging from a mild flu-like syndrome, to dengue fever, to life-threatening severe dengue diseases, including dengue hemorrhagic fever and dengue shock syndrome. There is currently no specific treatment for dengue diseases, and the molecular mechanism underlying dengue pathogenesis remains poorly understood. In this study, we combined biochemical, bioinformatics, high-content analysis and RNA sequencing approaches to characterize a highly conserved interface of the RNA genome of DENV with a human factor named DDX6 in infected cells. The significance of our research is in identifying the mechanism for a viral strategy to alter host cell fates, which conceivably allows us to generate a model for live-attenuated vaccine and the design of new therapeutic reagent for dengue diseases.

Autophagy, Unfolded Protein Response, and Neuropilin-1 Cross-Talk in SARS-CoV-2 Infection: What Can Be Learned from Other Coronaviruses

The COVID-19 pandemic is caused by the 2019-nCoV/SARS-CoV-2 virus. This severe acute respiratory syndrome is currently a global health emergency and needs much effort to generate an urgent practical treatment to reduce COVID-19 complications and mortality in humans. Viral infection activates various cellular responses in infected cells, including cellular stress responses such as unfolded protein response (UPR) and autophagy, following the inhibition of mTOR. Both UPR and autophagy mechanisms are involved in cellular and tissue homeostasis, apoptosis, innate immunity modulation, and clearance of pathogens such as viral particles. However, during an evolutionary arms race, viruses gain the ability to subvert autophagy and UPR for their benefit. SARS-CoV-2 can enter host cells through binding to cell surface receptors, including angiotensin-converting enzyme 2 (ACE2) and neuropilin-1 (NRP1). ACE2 blockage increases autophagy through mTOR inhibition, leading to gastrointestinal complications during SARS-CoV-2 virus infection. NRP1 is also regulated by the mTOR pathway. An increased NRP1 can enhance the susceptibility of immune system dendritic cells (DCs) to SARS-CoV-2 and induce cytokine storm, which is related to high COVID-19 mortality. Therefore, signaling pathways such as mTOR, UPR, and autophagy may be potential therapeutic targets for COVID-19. Hence, extensive investigations are required to confirm these potentials. Since there is currently no specific treatment for COVID-19 infection, we sought to review and discuss the important roles of autophagy, UPR, and mTOR mechanisms in the regulation of cellular responses to coronavirus infection to help identify new antiviral modalities against SARS-CoV-2 virus.