Influenza A virus-induced autophagy contributes to enhancement of virus infectivity by SOD1 downregulation in alveolar epithelial cells

Unveiling the intersection: ferroptosis in influenza virus infection

The influenza virus (IFV) imposes a considerable health and economic burden globally, requiring a comprehensive understanding of its pathogenic mechanisms. Ferroptosis, an iron-dependent lipid peroxidation cell death pathway, holds unique implications for the antioxidant defense system, with possible contributions to inflammation. This exploration focuses on the dynamic interplay between ferroptosis and the host defense against viruses, emphasizing the influence of IFV infections on the activation of the ferroptosis pathway. IFV causes different types of cell death, including apoptosis, necrosis, and ferroptosis. IFV-induced ferroptotic cell death is mediated by alterations in iron homeostasis, intensifying the accumulation of reactive oxygen species and promoting lipid peroxidation. A comprehensive investigation into the mechanism of ferroptosis in viral infections, specifically IFV, has great potential to identify therapeutic strategies. This understanding may pave the way for the development of drugs using ferroptosis inhibitors, presenting an effective approach to suppress viral infections.

The Roles of Endocytosis and Autophagy at the Cellular Level During Influenza Virus Infection: A Mini-Review

Acute respiratory infections contribute to morbidity and mortality worldwide. The common cause of this deadly disease is a virus, and one of the most commonly found is the influenza virus. Influenza viruses have several capabilities in infection, including utilizing the host's machinery to survive within cells and replicate safely. This review aims to examine the literature on how influenza viruses use host machinery, including endocytosis and autophagy, for their internalization and replication within cells. This review method involves a literature search by examining articles published in the PubMed and Scopus databases. The keywords used were "Endocytosis" OR "Autophagy" AND "Influenza Virus". Eighteen articles were included due to inclusion and exclusion criteria. GTPases switch, and V-ATPase plays a key role in the endocytic machinery hijacked by influenza viruses to enter host cells. On the other hand, LC3 and Atg5 facilitate influenza-induced apoptosis via the autophagic pathway. In conclusion, influenza viruses primarily use clathrin-mediated endocytosis to enter cells and avoid degradation during endosomal maturation by exiting endosomes for transfer to the nucleus for replication. It also uses autophagy to induce apoptosis to continue replication. The capability of the influenza viruses to hijack endocytosis and autophagy mechanisms could be critical points for further research. Therefore, we discuss how the influenza virus utilizes both endocytosis and autophagy and the approach for a new strategic therapy targeting those mechanisms.

The critical role of RAGE in severe influenza infection: A target for control of inflammatory response in the disease

Controlling the excessive inflammatory response is one of the key ways to reduce the severity and mortality of severe influenza virus infections. RAGE is involved in inflammatory responses and acute lung injuries. Here, we investigated the role of RAGE and its potential application as a target for severe influenza treatment through serological correlation analysis for influenza patients, and treatment with the RAGE inhibitor FPS-ZM1 on A549 cells or mice with influenza A (H1N1) infection. The results showed high levels of RAGE were correlated with immunopathological injury and severity of influenza, and FPS-ZM1 treatment increased the viability of A549 cells with influenza A infection and decreased morbidity and mortality of influenza A virus infection in mice. The RAGE/NF-κb inflammatory signaling pathway is a major targeting pathway for FPS-ZM1 treatment in severe influenza. These findings provide further insights into the immune injury of severe influenza and a potential targeting candidate for the disease treatment.

Triggering Degradation of Host Cellular Proteins for Robust Propagation of Influenza Viruses

Following infection, influenza viruses strive to establish a new host cellular environment optimized for efficient viral replication and propagation. Influenza viruses use or hijack numerous host factors and machinery not only to fulfill their own replication process but also to constantly evade the host's antiviral and immune response. For this purpose, influenza viruses appear to have formulated diverse strategies to manipulate the host proteins or signaling pathways. One of the most effective tactics is to specifically induce the degradation of the cellular proteins that are detrimental to the virus life cycle. Here, we summarize the cellular factors that are deemed to have been purposefully degraded by influenza virus infection. The focus is laid on the mechanisms for the protein ubiquitination and degradation in association with facilitated viral amplification. The fate of influenza viral infection of hosts is heavily reliant on the outcomes of the interplay between the virus and the host antiviral immunity. Understanding the processes of how influenza viruses instigate the protein destruction pathways could provide a foundation for the development of advanced therapeutics to target host proteins and conquer influenza.

The relationship between autophagy and respiratory viruses

Respiratory viruses have caused severe global health problems and posed essential challenges to the medical community. In recent years, the role of autophagy as a critical process in cells in viral respiratory diseases has been noticed. One of the vital catabolic biological processes in the body is autophagy. Autophagy contributes to energy recovery by targeting and selectively directing foreign microorganisms, organelles, and senescent intracellular proteins to the lysosome for degradation and phagocytosis. Activation or suppression of autophagy is often initiated when foreign pathogenic organisms such as viruses infect cells. Because of its antiviral properties, several viruses may escape or resist this process by encoding viral proteins. Viruses can also use autophagy to enhance their replication or prolong the persistence of latent infections. Here, we provide an overview of autophagy and respiratory viruses such as coronavirus, rhinovirus, parainfluenza, influenza, adenovirus, and respiratory syncytial virus, and examine the interactions between them and the role of autophagy in the virus-host interaction process and the resulting virus replication strategy.

The interplay between copper metabolism and microbes: in perspective of host copper-dependent ATPases ATP7A/B

Copper, a vital element in various physiological processes, is transported from the gastrointestinal tract to tissues and cells through diverse copper transporters. Among these transporters, ATP7A and ATP7B play significant roles in regulating systemic copper metabolism and exhibit precise regulation in their intracellular trafficking. These transporters undergo dynamic shuttling between the trans-Golgi network (TGN) and the plasma membrane via the endocytic recycling mechanism, which involves the retromer and other associated factors. Interestingly, the antimicrobial attribute of copper implies a potential connection between microbial infection and copper metabolism. Several microbes, including Salmonella enterica, Cryptococcus, Influenza A virus (IAV) and Zika virus (ZIKV) have been observed to impact the regulatory mechanisms of ATP7A/B, either directly or indirectly, as a means of survival. This review summarizes the key features and trafficking mechanisms of the copper transporters ATP7A/B, and examines the intricate interplay between microbes and copper metabolism. Ultimately, it highlights how microbes can perturb copper homeostasis through interactions with host factors, offering valuable insights into the mechanistic aspects of host-microbe interactions.

The battle for autophagy between host and influenza A virus

Influenza A virus (IAV) is an infectious pathogen, threatening the population and public safety with its epidemics. Therefore, it is essential to better understand influenza virus biology to develop efficient strategies against its pathogenicity. Autophagy is an important cellular process to maintain cellular homeostasis by cleaning up the hazardous substrates in lysosome. Accumulating research has also suggested that autophagy is a critical mechanism in host defense responses against IAV infection by degrading viral particles and activating innate or acquired immunity to induce viral clearance. However, IAV has conversely hijacked autophagy to strengthen virus infection by blocking autophagy maturation and further interfering host antiviral signalling to promote viral replication. Therefore, how the battle for autophagy between host and IAV is carried out need to be known. In this review, we describe the role of autophagy in host defence and IAV survival, and summarize the role of influenza proteins in subverting the autophagic process as well as then concentrate on how host utilize antiviral function of autophagy to prevent IAV infection.

Swine influenza virus triggers ferroptosis in A549 cells to enhance virus replication

Background

Recently, Influenza A virus (IAV) has been shown to activate several programmed cell death pathways that play essential roles in host defense. Indeed, cell death caused by viral infection may be mediated by a mixed pattern of cell death instead of a certain single mode. Ferroptosis is a novel form of regulated cell death (RCD) that is mainly mediated by iron-dependent lipid peroxidation. Based on the proteomic data, we wondered whether IAV causes ferroptosis in host cells.

Method

In this study, a quantitative proteomics approach based on an iTRAQ combined with LC–MS/MS was used to profile proteins expressed in A549 cells infected with H1N1 swine influenza virus (SIV). Meanwhile, we measured the intracellular iron content, reactive oxygen species (ROS) release and lipid peroxidation in response to SIV infection. Finally, a drug experiment was conducted to investigate the effects of ferroptosis on modulating SIV survival.

Results

The bioinformatics analysis revealed several proteins closely relevant to iron homeostasis and transport, and the ferroptosis signaling pathway are highly enriched in response to SIV infection. In our experiment, aberrant expression of iron-binding proteins disrupted labile iron uptake and storage after SIV infection. Meanwhile, SIV infection inhibited system the Xc⁻/GPX4 axis resulting in GSH depletion and the accumulation of lipid peroxidation products. Notably, cell death caused by SIV as a result of iron-dependent lipid peroxidation can be partially rescued by ferroptosis inhibitor. Additionally, blockade of the ferroptotic pathway by ferrostatin-1 (Fer-1) treatment decreased viral titers and inflammatory response.

Conclusions

This study revealed a new mode of cell death induced by IAV infection, and our findings might improve the understanding of the underlying mechanism involved in the interaction of virus and host cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-022-01825-y.

Serum superoxide dismutase level is a potential biomarker of disease prognosis in patients with hemorrhagic fever with renal syndrome caused by the Hantaan virus

Background

Hemorrhagic fever with renal syndrome (HFRS) is a disease with increased systemic inflammation and a high fatality rate. Oxidative stress is crucial for inflammation in the pathogeneses of various diseases. We aimed to identify biomarkers of oxidative stress that may assess the severity and disease outcomes of patients with HFRS.

Methods

Between January 2015 and September 2018, we analyzed a retrospective cohort of 149 HFRS patients and 30 healthy individuals. Serum levels of SOD were measured using an ELISA commercial kit, and survival analysis was carried out using the Kaplan–Meier method.

Results

Patients with HFRS had significantly lower serum SOD levels compared with healthy controls (108.40 ± 2.47 U/mL vs 164.23 ± 3.82 U/mL, P < 0.01). SOD levels in patients were lower at acute than at convalescent stage (108.40 ± 2.47 U/mL vs 138.27 ± 2.87 U/mL, P < 0.01), and in severe and critical patients than in moderate and mild patients (89.63 ± 2.38 U/mL vs 122.53 ± 3.18 U/mL, P < 0.01). A serum level of SOD < 88.6 U/mL at admission was associated with a significant increase in mortality risk in HFRS patients.

Conclusion

Our results indicate that serum levels of SOD measured at admission can be used to assess disease severity and assign patients into high- and low-risk groups. SOD can be considered a novel biomarker of severity and outcomes in patients with HFRS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07394-3.

The Multi-Faceted Role of Autophagy During Animal Virus Infection

Autophagy is a process of degradation to maintain cellular homeostatic by lysosomes, which ensures cellular survival under various stress conditions, including nutrient deficiency, hypoxia, high temperature, and pathogenic infection. Xenophagy, a form of selective autophagy, serves as a defense mechanism against multiple intracellular pathogen types, such as viruses, bacteria, and parasites. Recent years have seen a growing list of animal viruses with autophagy machinery. Although the relationship between autophagy and human viruses has been widely summarized, little attention has been paid to the role of this cellular function in the veterinary field, especially today, with the growth of serious zoonotic diseases. The mechanisms of the same virus inducing autophagy in different species, or different viruses inducing autophagy in the same species have not been clarified. In this review, we examine the role of autophagy in important animal viral infectious diseases and discuss the regulation mechanisms of different animal viruses to provide a potential theoretical basis for therapeutic strategies, such as targets of new vaccine development or drugs, to improve industrial production in farming.

The Crossroads between Host Copper Metabolism and Influenza Infection

Three main approaches are used to combat severe viral respiratory infections. The first is preemptive vaccination that blocks infection. Weakened or dead viral particles, as well as genetic constructs carrying viral proteins or information about them, are used as an antigen. However, the viral genome is very evolutionary labile and changes continuously. Second, chemical agents are used during infection and inhibit the function of a number of viral proteins. However, these drugs lose their effectiveness because the virus can rapidly acquire resistance to them. The third is the search for points in the host metabolism the effect on which would suppress the replication of the virus but would not have a significant effect on the metabolism of the host. Here, we consider the possibility of using the copper metabolic system as a target to reduce the severity of influenza infection. This is facilitated by the fact that, in mammals, copper status can be rapidly reduced by silver nanoparticles and restored after their cancellation.

Reactive oxygen species as potential antiviral targets

Reactive oxygen species (ROS) are by-products of cellular metabolism and can be either beneficial, at low levels, or deleterious, at high levels, to the cell. It is known that several viral infections can increase oxidative stress, which is mainly facilitated by viral-induced imbalances in the antioxidant defence mechanisms of the cell. While the exact role of ROS in certain viral infections (adenovirus and dengue virus) remains unknown, other viruses can use ROS for enhancement of pathogenesis (SARS coronavirus and rabies virus) or replication (rhinovirus, West Nile virus and vesicular stomatitis virus) or both (hepatitis C virus, human immunodeficiency virus and influenza virus). While several viral proteins (mainly for hepatitis C and human immunodeficiency virus) have been identified to play a role in ROS formation, most mediators of viral ROS modulation are yet to be elucidated. Treatment of viral infections, including hepatitis C virus, human immunodeficiency virus and influenza virus, with ROS inhibitors has shown a decrease in both pathogenesis and viral replication both in vitro and in animal models. Clinical studies indicating the potential for targeting ROS-producing pathways as possible broad-spectrum antiviral targets should be evaluated in randomized controlled trials.

Immune profiles of male giant panda (Ailuropoda melanoleuca) during the breeding season

Background

The giant panda (Ailuropoda melanoleuca) is a threatened endemic Chinese species and a flagship species of national and global conservation concern. Life history theory proposes that reproduction and immunity can be mutually constraining and interrelated. Knowledge of immunity changes of male giant pandas during the breeding season is limited.

Results

Here, we researched peripheral blood gene expression profiles associated with immunity. Thirteen captive giant pandas, ranging from 9 to 11 years old, were divided into two groups based on their reproductive status. We identified 318 up-regulated DEGs and 43 down-regulated DEGs, which were enriched in 87 GO terms and 6 KEGG pathways. Additionally, we obtained 45 immune-related genes with altered expression, mostly up-regulated, and identified four hub genes HSPA4, SUGT1, SOD1, and IL1B in PPI analysis. These 45 genes were related to pattern recognition receptors, autophagy, peroxisome, proteasome, natural killer cell, antigen processing and presentation. SUGT1 and IL1B were related to pattern recognition receptors. HSP90AA1 was the most up-regulated gene and is a member of heat shock protein 90 family. HSP90 contributes to the translocation of extracellular antigen. KLRD1 encodes CD94, whose complex is an inhibitor of the cytotoxic activity of NK cells, was down-regulated. IGIP, which has the capability of inducing IgA production by B cells, was down-regulated, suggesting low concentration of IgA in male giant pandas. Our results suggest that most immune-related genes were up-regulated and more related to innate immune than adaptive immune.

Conclusions

Our results indicated that breeding male giant pandas presented an immunoenhancement in innate immunity, enhanced antigen presentation and processing in cellular immunity compared to non-breeding males. The humoral immunity of male giant pandas may show a tendency to decrease during the breeding season. This study will provide a foundation for further studies of immunity and reproduction in male giant pandas.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07456-x.

Autophagy is involved in the replication of H9N2 influenza virus via the regulation of oxidative stress in alveolar epithelial cells

Background

Oxidative stress is an important pathogenic factor in influenza A virus infection. It has been found that reactive oxygen species induced by the H9N2 influenza virus is associated with viral replication. However, the mechanisms involved remain to be elucidated.

Methods

In this study, the role of autophagy was investigated in H9N2 influenza virus-induced oxidative stress and viral replication in A549 cells. Autophagy induced by H9N2 was inhibited by an autophagy inhibitor or RNA interference, the autophagy level, viral replication and the presence of oxidative stress were detected by western blot, TCID50 assay, and Real-time PCR. Then autophagy and oxidative stress were regulated, and viral replication was determined. At last, the Akt/TSC2/mTOR signaling pathways was detected by western blot.

Results

Autophagy was induced by the H9N2 influenza virus and the inhibition of autophagy reduced the viral titer and the expression of nucleoprotein and matrix protein. The blockage of autophagy suppressed the H9N2 virus-induced increase in the presence of oxidative stress, as evidenced by decreased reactive oxygen species production and malonaldehyde generation, and increased superoxide dismutase 1 levels. The changes in the viral titer and NP mRNA level caused by the antioxidant, N-acetyl-cysteine (NAC), and the oxidizing agent, H₂O₂, confirmed the involvement of oxidative stress in the control of viral replication. NAC plus transfection with Atg5 siRNA significantly reduced the viral titer and oxidative stress compared with NAC treatment alone, which confirmed that autophagy was involved in the replication of H9N2 influenza virus by regulating oxidative stress. Our data also revealed that autophagy was induced by the H9N2 influenza virus through the Akt/TSC2/mTOR pathway. The activation of Akt or the inhibition of TSC2 suppressed the H9N2 virus-induced increase in the level of LC3-II, restored the decrease in the expression of phospho-pAkt, phospho-mTOR and phospho-pS6 caused by H9N2 infection, suppressed the H9N2-induced increase in the presence of oxidative stress, and resulted in a decrease in the viral titer.

Conclusion

Autophagy is involved in H9N2 virus replication by regulating oxidative stress via the Akt/TSC2/mTOR signaling pathway. Thus, autophagy maybe a target which may be used to improve antiviral therapeutics.

Threonyl-tRNA Synthetase Promotes T Helper Type 1 Cell Responses by Inducing Dendritic Cell Maturation and IL-12 Production via an NF-κB Pathway

Threonyl-tRNA synthetase (TRS) is an aminoacyl-tRNA synthetase that catalyzes the aminoacylation of tRNA by transferring threonine. In addition to an essential role in translation, TRS was extracellularly detected in autoimmune diseases and also exhibited pro-angiogenetic activity. TRS is reported to be secreted into the extracellular space when vascular endothelial cells encounter tumor necrosis factor-α. As T helper (Th) type 1 response and IFN-γ levels are associated with autoimmunity and angiogenesis, in this study, we investigated the effects of TRS on dendritic cell (DC) activation and CD4 T cell polarization. TRS-treated DCs exhibited up-regulated expression of activation-related cell-surface molecules, including CD40, CD80, CD86, and MHC class II. Treatment of DCs with TRS resulted in a significant increase of IL-12 production. TRS triggered nuclear translocation of the NF-κB p65 subunit along with the degradation of IκB proteins and the phosphorylation of MAPKs in DCs. Additionally, MAPK inhibitors markedly recovered the degradation of IκB proteins and the increased IL-12 production in TRS-treated DCs, suggesting the involvement of MAPKs as the upstream regulators of NF-κB in TRS-induced DC maturation and activation. Importantly, TRS-stimulated DCs significantly increased the populations of IFN-γ⁺CD4 T cells, and the levels of IFN-γ when co-cultured with CD4⁺ T cells. The addition of a neutralizing anti-IL-12 mAb to the cell cultures of TRS-treated DCs and CD4⁺ T cells resulted in decreased IFN-γ production, indicating that TRS-stimulated DCs may enhance the Th1 response through DC-derived IL-12. Injection of OT-II mice with OVA-pulsed, TRS-treated DCs also enhanced Ag-specific Th1 responses in vivo. Importantly, injection with TRS-treated DC exhibited increased populations of IFN-γ⁺-CD4⁺ and -CD8⁺ T cells as well as secretion level of IFN-γ, resulting in viral clearance and increased survival periods in mice infected with influenza A virus (IAV), as the Th1 response is associated with the enhanced cellular immunity, including anti-viral activity. Taken together, these results indicate that TRS promotes the maturation and activation of DCs, DC-mediated Th1 responses, and anti-viral effect on IAV infection.

Anti-Influenza Effect of Nanosilver in a Mouse Model

The present study assesses copper metabolism of the host organism as a target of antiviral strategy, basing on the "virocell" concept. Silver nanoparticles (AgNPs) were used as a specific active agent because they reduce the level of holo-ceruloplasmin, the main extracellular cuproenzyme. The mouse model of influenza virus A infection was used with two doses: 1 LD₅₀ and 10 LD₅₀. Three treatment regimens were used: Scheme 1-mice were pretreated 4 days before infection and then every day during infection development; Scheme 2-mice were pretreated four days before infection and on the day of virus infection; Scheme 3-virus infection and AgNP treatment started simultaneously, and mice were injected with AgNPs until the end of the experiment. The mice treated by Scheme 1 demonstrated significantly lower mortality, the protection index reached 60-70% at the end of the experiment, and mean lifespan was prolonged. In addition, the treatment of the animals with AgNPs resulted in normalization of the weight dynamics. Despite the amelioration of the infection, AgNP treatment did not influence influenza virus replication. The possibility of using nanosilver as an effective indirectly-acting antiviral drug is discussed.

Autophagy involved in antiviral activity of sodium tanshinone IIA sulfonate against porcine reproductive and respiratory syndrome virus infection in vitro

BACKGROUND

In previous research, we have demonstrated that sodium tanshinone IIA sulfonate (STS) has anti-porcine reproductive and respiratory syndrome virus (PRRSV) activity, but whether autophagy is involved in this process is still unknown. In this study, the autophagy effect of STS against PRRSV infection was investigated in vitro.

METHODS

Quantitative real-time PCR (qRT-PCR) and western blot was used to evaluate the inhibition ability of STS on the mRNA expression levels on cell autophagy genes, that is Beclin1, ATG5 and ATG7. Simultaneously, the effect of STS on N protein/gene expression was assessed by indirect immuno-fluorescence assay (IFA), qRT-PCR and western blot.

RESULTS

The results indicated that STS inhibits autophagy induced by PRRSV. In addition, STS effectively suppresses PRRSV's N protein replication and N gene expression in Marc-145 cells infected with PRRSV in a time-dependent manner.

CONCLUSIONS

Our results suggest that STS exhibits anti-PRRSV activity in vitro by suppressing autophagy-related genes, which may provide a theoretical basis for further pharmacological agent development regarding PRRSV infection.

Induction of a 5-lipoxygenase product by daidzein is involved in the regulation of influenza virus replication

This study was conducted to evaluate the regulation mechanism of influenza virus replication following treatment of Madin-Darby canine kidney cells with the soy isoflavone daidzein. We performed comparative qualitative and quantitative analyses of lipid peroxide between mock-infected and virus-infected cells treated with or without daidzein, as it had been reported that daidzein was an antioxidant and lipid peroxide levels increased upon virus infection. Contrary to our belief, lipid peroxides were not elevated in virus-infected cells and no decrease in lipid peroxides was observed in daidzein-treated cells. In daidzein-treated cells, 5-hydroxyeicosatetraenoic acid, the 5-lipoxygenase product derived from arachidonate, was significantly elevated compared to other lipid peroxides. Zileuton (5-lipoxygenase inhibitor) and 5-lipoxygenase knockdown reduced the daidzein-induced antiviral effect. Moreover, virus replication was regulated by treatment with 5-hydroperoxyeicosatetraenoic acid, a precursor of 5-hydroxyeicosatetraenoic acid and 5-lipoxygenase primary product. These results suggest that daidzein regulates virus replication via signal transduction through 5-lipoxygenase products.

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.

Resveratrol‑loaded nanoparticles inhibit enterovirus 71 replication through the oxidative stress‑mediated ERS/autophagy pathway

A number of studies have demonstrated that resveratrol (RES) has a variety of biological functions, including cardiovascular protective effects, treatment of mutations, and anti‑inflammatory, anti‑tumor and antiviral effects. In the present study, RES‑loaded nanoparticles (RES‑NPs) were used to protect rhabdosarcoma (RD) cells from enterovirus 71 (EV71) infection, and the relevant mechanisms were also explored. An amphiphilic copolymer, monomethoxy poly (ethylene glycol)‑b‑poly (D,L‑lactide), was used as vehicle material, and RES‑NPs with necessitated drug‑loading content and suitable sizes were prepared under optimized conditions. RES‑NPs exhibited the ability to inhibit the increase of intracellular oxidative stress. The prospective mechanism for the function of RES‑NPs suggested was that RES‑NPs may inhibit the oxidative stress‑mediated PERK/eIF2α/ATF4 signaling pathway, downregulate the autophagy pathway and resist EV71‑induced RD cells injury. Furthermore, RES‑NPs treatment markedly inhibited the secretion of inflammatory factors, including interleukin (IL)‑6, IL‑8 and tumor necrosis factor‑α elicited by EV71 infection. Concomitantly, inhibitors of oxidative stress, endoplasmic reticulum stress (ERS) or autophagy were demonstrated to negate the anti‑inflammatory and antiviral effects of RES‑NPs on EV71‑infected RD cells. These results demonstrated that RES‑NPs attenuated EV71‑induced viral replication and inflammatory effects by inhibiting the oxidative stress‑mediated ERS/autophagy signaling pathway. In view of their safety and efficiency, these RES‑NPs have potential applications in protecting RD cells from EV71 injury.

Endoplasmic reticulum-associated degradation potentiates the infectivity of influenza A virus by regulating the host redox state

During influenza A virus (IAV) infection, significant effects of oxidative stress often emerge due to the disruption of the redox balance. Reactive oxygen species (ROS) generated during IAV infection have been known to exert various effects on both the virus and host tissue. However, the mechanisms underlying the accumulation of ROS and their physiological significance in IAV infection have been extensively studied but remain to be fully understood. Here, we show that the levels of Sp1, a key controller of Cu-Zn superoxide dismutase (SOD1) gene expression, and SOD1 are mainly dependent upon the activity of X-box-binding protein 1 (XBP1), which is a downstream factor of the endoplasmic reticulum (ER) transmembrane sensor inositol-requiring enzyme 1 (IRE1) during ER stress. In IRE1-deficient mouse embryo fibroblasts (MEFs) or A549 human lung cells treated with XBP1 siRNA, IAV-induced Sp1 loss was mitigated. However, overexpression of the spliced form of XBP1 in IRE1-deficient MEFs resulted in a further decrease in Sp1 levels, whereas the unspliced form showed no significant differences. Treatment with proteasome inhibitor MG132 markedly inhibited the IRE1/XBP1-mediated loss of Sp1 and SOD, suggesting the involvement of proteasome-dependent ER-associated degradation (ERAD). The increase in SOD1 levels with the expression of siRNA-targeting p97, a central component of the ubiquitin-proteasome system, supports the major role of the ERAD process in IAV-mediated SOD1 loss. In addition, ROS generation due to IAV infection was attenuated in cells lacking either IRE1 or JNK. These results reveal the important roles of both IRE1/XBP1-mediated ERAD and the JNK pathway in IAV infection. Interestingly, the increase in ROS due to IAV infection is correlated with the increase in the virus titer in vitro and in vivo. However, 4-phenylbutyrate (4-PBA), an inhibitor of ER stress signaling, weakened the effect of IAV infection on SOD1 loss in a dose-dependent manner. Furthermore, the treatment of mice with 4-PBA efficiently attenuated ROS generation and ER stress in lung tissue and eventually lowered the IAV titer. These results strongly suggest that the ERAD process plays a major role in IAV infection, thus making it a potential target for antiviral drug therapy.

Circular RNA GATAD2A promotes H1N1 replication through inhibiting autophagy

Circular RNAs (circRNAs) play critical roles in various diseases. However, whether and how circular RNA regulates influenza A virus (IAV) infection is unknown. Here, we studied the role of circular RNA GATA Zinc Finger Domain Containing 2A (circ-GATAD2A) in the replication of IAV H1N1 in A549 cells. Circ-GATAD2A was formed upon H1N1 infection. Knockdown of circ-GATAD2A in A549 cells enhanced autophagy and inhibited H1N1 replication. By contrast, overexpression of circ-GATAD2A impaired autophagy and promoted H1N1 replication. Similarly, knockout of vacuolar protein sorting 34 (VPS34) blocked autophagy and increased H1N1 replication. However, the expression of circ-GATAD2A could not further enhance H1N1 replication in VPS34 knockout cells. Collectively, these data indicated that circ-GATAD2A promotes the replication of H1N1 by inhibiting autophagy.

Glutamine starvation inhibits snakehead vesiculovirus replication via inducing autophagy associated with the disturbance of endogenous glutathione pool

Autophagy is a degradation cellular process which also plays an important role in virus infection. Glutamine is an essential substrate for the synthesis of glutathione which is the most abundant thiol-containing compound within the cells and plays a key role in the antioxidant defense and intracellular signaling. There is an endogenous cellular glutathione pool which consists of two forms of glutathione, i.e. the reduced form (GSH) and the oxidized form (GSSG). GSH serves as an intracellular antioxidant to maintain cellular redox homeostasis by scavenging free radicals and other reactive oxygen species (ROS) which can lead to autophagy. Under physiological conditions, the concentration of GSSG is only about 1% of total glutathione, while stress condition can result in a transient increase of GSSG. In our previous report, we showed that the replication of snakehead fish vesiculovirus (SHVV) was significant inhibited in SSN-1 cells cultured in the glutamine-starvation medium, however the underlying mechanism remains enigmatic. Here, we revealed that the addition of L-Buthionine-sulfoximine (BSO), a specific inhibitor of the GSH synthesis, could decrease the γ-glutamate-cysteine ligase (GCL) activity and GSH levels, resulting in autophagy and significantly inhibition of the replication of SHVV in SSN-1 cells cultured in the complete medium. On the other hand, the replication of SHVV was rescued and the autophagy was inhibited in the SSN-1 cells cultured in the glutamine-starvation medium supplemented with additional GSH. Furthermore, the inhibition of the synthesis of GSH had not significantly affected the generation of reactive oxygen species (ROS). However, it significantly decreased level of GSH and enhanced the level of GSSG, resulting in the decrease of the value of GSH/GSSG, indicating that it promoted the cellular oxidative stress. Overall, the present study demonstrated that glutamine starvation impaired the replication of SHVV in SSN-1 cells via inducing autophagy associated with the disturbance of the endogenous glutathione pool.

Cisplatin induces autophagy to enhance hepatitis B virus replication via activation of ROS/JNK and inhibition of the Akt/mTOR pathway

Chronic hepatitis B virus (HBV) infection remains a serious global health concern. Cisplatin is a chemotherapeutic agent commonly used to treat various cancers. However, HBV-infected patients receiving chemotherapy are at risk of HBV reactivation via unknown mechanisms, which we aimed to elucidate in this study. We found that autophagy plays a central role in cisplatin-induced HBV replication. Cisplatin treatment induced autophagy in both HBV-replicating cells and an HBV-transgenic mouse model as evident from marked upregulation of microtubule-associated protein 1 light chain 3 (LC3)-II and the accumulation of red fluorescent protein (RFP)-LC3 puncta. Cisplatin induced complete autophagic flux, which was detected via monitoring of p62 degradation and RFP-GFP-LC3 expression. Inhibition of autophagy by chloroquine, 3-methyladenine, or Atg5 knockdown significantly attenuated cisplatin-induced HBV replication. Additionally, cisplatin-induced autophagy could be significantly attenuated by using the ROS scavenger N-acetyl-l-cysteine. Mechanically, cisplatin promoted HBV replication and autophagy through ROS/JNK and AKT/mTOR signaling. Inhibition of JNK or activation of Akt/mTOR signaling reversed cisplatin-mediated autophagy and HBV replication promotion. In contrast, suppression of Akt/mTOR signaling further promoted cisplatin-induced HBV replication. Finally, pharmacotherapeutic inhibition of autophagy or ROS production impaired HBV production induced by cisplatin in vivo. Together, our results indicate that ROS/JNK and mTOR/AKT-mediated autophagy plays an important role in cisplatin-induced HBV reactivation.

Autophagy and pulmonary disease

Autophagy is a process of cell self-renewal that is dependent on the degradation of the cytoplasmic proteins or organelles of lysosomes. Many diseases, such as metabolic diseases, cancer, neurodegenerative diseases, and lung diseases, have been confirmed to be associated with elevated or impaired levels of autophagy. At present, studies have found that autophagy participates in the regulation of chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis, pulmonary hypertension, acute lung injury, lung cancer, and other pulmonary diseases. Using recent literature on the signal transduction mechanisms of autophagy and the effects of autophagy signalling on lung diseases, this review intends to clarify the mechanisms of lung disease to guide the treatment of related diseases. The reviews of this paper are available via the supplemental material section.