Autophagy benefits the replication of Newcastle disease virus in chicken cells and tissues. J Virol. 2014;88:525-537. [PMID: 24173218 DOI: 10.1128/jvi.01849-13]

Hypervirulent fowl adenovirus serotype 4 elicits early innate immune response and promotes virus-induced cellular autophagy in the spleen

The recent emergence of hepatitis-hydropericardium syndrome caused by highly pathogenic fowl adenovirus serotype 4 (FAdV-4) has resulted in significant economic losses to the poultry industry. However, the early innate immune response of immune organs within 24 hpi and the induction of autophagy in vivo after FAdV-4 infection have not been fully elucidated. In this study, 35-day-old specific pathogen-free (SPF) chickens were artificially infected with hypervirulent FAdV-4, which resulted in a mortality rate of up to 90%. The results showed that FAdV-4 infection rapidly triggered the innate immune response in vivo of chickens, with the spleen eliciting a stronger innate immune response than the thymus and bursa. During the early stage of viral infection within 24 hpi, the main receptors TLR3/7/21, MDA5, and cGAS were activated via the NF-κB and TBK1/IRF7-dependent signaling pathways, which up-regulated production of inflammatory cytokines and type I interferons. Additionally, the expression levels of the autophagy-related molecules LC3B, Beclin1, and ATG5 were significantly up-regulated at 24 hpi, while degradation of SQSTM1/p62 was observed, suggesting that FAdV-4 infection elicits a complete autophagy response in the spleen. Besides, the colocalization of Fiber2 and LC3B suggested that FAdV-4 infection induced autophagy which benefits FAdV-4 replication in vivo. This study provides new insights into the immunoregulation signal pathways of the early innate immunity in response to hypervirulent FAdV-4 infection in vivo within 24 hpi and the close relationship between viral replication and autophagy.

The Application of Newcastle Disease Virus (NDV): Vaccine Vectors and Tumor Therapy

Newcastle disease virus (NDV) is an avian pathogen with an unsegmented negative-strand RNA genome that belongs to the Paramyxoviridae family. While primarily pathogenic in birds, NDV presents no threat to human health, rendering it a safe candidate for various biomedical applications. Extensive research has highlighted the potential of NDV as a vector for vaccine development and gene therapy, owing to its transcriptional modularity, low recombination rate, and lack of a DNA phase during replication. Furthermore, NDV exhibits oncolytic capabilities, efficiently eliciting antitumor immune responses, thereby positioning it as a promising therapeutic agent for cancer treatment. This article comprehensively reviews the biological characteristics of NDV, elucidates the molecular mechanisms underlying its oncolytic properties, and discusses its applications in the fields of vaccine vector development and tumor therapy.

The Ca2+-dependent phosphatase calcineurin dephosphorylates TBK1 to suppress antiviral innate immunity

Tumor necrosis factor receptor-associated factor family member-associated NF-κB activator-binding kinase 1 (TBK1) plays a key role in the induction of the type 1 interferon (IFN-I) response, which is an important component of innate antiviral defense. Viruses target calcium (Ca2+) signaling networks, which participate in the regulation of the viral life cycle, as well as mediate the host antiviral response. Although many studies have focused on the role of Ca2+ signaling in the regulation of IFN-I, the relationship between Ca2+ and TBK1 in different infection models requires further elucidation. Here, we examined the effects of the Newcastle disease virus (NDV)-induced increase in intracellular Ca2+ levels on the suppression of host antiviral responses. We demonstrated that intracellular Ca2+ increased significantly during NDV infection, leading to impaired IFN-I production and antiviral immunity through the activation of calcineurin (CaN). Depletion of Ca²+ was found to lead to a significant increase in virus-induced IFN-I production resulting in the inhibition of viral replication. Mechanistically, the accumulation of Ca2+ in response to viral infection increases the phosphatase activity of CaN, which in turn dephosphorylates and inactivates TBK1 in a Ca2+-dependent manner. Furthermore, the inhibition of CaN on viral replication was counteracted in TBK1 knockout cells. Together, our data demonstrate that NDV hijacks Ca2+ signaling networks to negatively regulate innate immunity via the CaN-TBK1 signaling axis. Thus, our findings not only identify the mechanism by which viruses exploit Ca2+ signaling to evade the host antiviral response but also, more importantly, highlight the potential role of Ca2+ homeostasis in the viral innate immune response.IMPORTANCEViral infections disrupt intracellular Ca2+ homeostasis, which affects the regulation of various host processes to create conditions that are conducive for their own proliferation, including the host immune response. The mechanism by which viruses trigger TBK1 activation and IFN-I induction through viral pathogen-associated molecular patterns has been well defined. However, the effects of virus-mediated Ca2+ imbalance on the IFN-I pathway requires further elucidation, especially with respect to TBK1 activation. Herein, we report that NDV infection causes an increase in intracellular free Ca2+ that leads to activation of the serine/threonine phosphatase CaN, which subsequently dephosphorylates TBK1 and negatively regulates IFN-I production. Furthermore, depletion of Ca2+ or inhibition of CaN activity exerts antiviral effects by promoting the production of IFN-I and inhibiting viral replication. Thus, our results reveal the potential role of Ca2+ in the innate immune response to viruses and provide a theoretical reference for the treatment of viral infectious diseases.

Long Non-Coding RNA Analysis: Severe Pathogenicity in Chicken Embryonic Visceral Tissues Infected with Highly Virulent Newcastle Disease Virus-A Comparison to the Avirulent Vaccine Virus

There are significant variations in pathogenicity among different virulent strains of the Newcastle disease virus (NDV). Virulent NDV typically induces severe pathological changes and high mortality rates in infected birds, while avirulent NDV usually results in asymptomatic infection. Currently, the understanding of the specific mechanisms underlying the differences in host pathological responses and symptoms caused by various virulent NDV strains remains limited. Long non-coding RNA (lncRNA) can participate in a range of biological processes and plays a crucial role in viral infection and replication. Therefore, this study employed RNA-Seq to investigate the transcriptional profiles of chicken embryos' visceral tissues (CEVTs) infected with either the virulent NA-1 strain or avirulent LaSota strain at 24 hpi and 36 hpi. Using bioinformatic methods, we obtained a total of 2532 lncRNAs, of which there were 52 and 85 differentially expressed lncRNAs at 24 hpi and 36 hpi, respectively. LncRNA analysis revealed that the severe pathological changes and symptoms induced by virulent NDV infection may be partially attributed to related target genes, regulated by differentially expressed lncRNAs such as MSTRG.1545.5, MSTRG.14601.6, MSTRG.7150.1, and MSTRG.4481.1. Taken together, these findings suggest that virulent NDV infection exploits the host's metabolic resources and exerts an influence on the host's metabolic processes, accompanied by excessive activation of the immune response. This impacts the growth and development of each system of CEVTs, breaches the blood-brain barrier, inflicts severe damage on the nervous system, and induces significant lesions. These observations may be attributed to variations in pathology. Consequently, novel insights were obtained into the intricate regulatory mechanisms governing NDV and host interactions. This will aid in unraveling the molecular mechanisms underlying both virulent and avirulent forms of NDV infection.

Viruses and autophagy: bend, but don't break

Autophagy is a constitutive cellular process of degradation required to maintain homeostasis and turn over spent organelles and aggregated proteins. For some viruses, the process can be antiviral, degrading viral proteins or virions themselves. For many other viruses, the induction of the autophagic process provides a benefit and promotes viral replication. In this Review, we survey the roles that the autophagic pathway plays in the replication of viruses. Most viruses that benefit from autophagic induction block autophagic degradation, which is a 'bend, but don't break' strategy initiating but limiting a potentially antiviral response. In almost all cases, it is other effects of the redirected autophagic machinery that benefit these viruses. This rapid mechanism to generate small double-membraned vesicles can be usurped to shape membranes for viral genome replication and virion maturation. However, data suggest that autophagic maintenance of cellular homeostasis is crucial for the initiation of infection, as viruses have evolved to replicate in normal, healthy cells. Inhibition of autophagic degradation is important once infection has initiated. Although true degradative autophagy is probably a negative for most viruses, initiating nondegradative autophagic membranes benefits a wide variety of viruses.

Oncolytic Newcastle disease virus induced degradation of YAP through E3 ubiquitin ligase PRKN to exacerbate ferroptosis in tumor cells

Ferroptosis, a form of programmed cell death characterized by iron-dependent lipid peroxidation, has recently gained considerable attention in the field of cancer therapy. There is significant crosstalk between ferroptosis and several classical signaling pathways, such as the Hippo pathway, which suppresses abnormal growth and is frequently aberrant in tumor tissues. Yes-associated protein 1 (YAP), the core effector molecule of the Hippo pathway, is abnormally expressed and activated in a variety of malignant tumor tissues. We previously proved that the oncolytic Newcastle disease virus (NDV) activated ferroptosis to kill tumor cells. NDV has been used in tumor therapy; however, its oncolytic mechanism is not completely understood. In this study, we demonstrated that NDV exacerbated ferroptosis in tumor cells by inducing ubiquitin-mediated degradation of YAP at Lys90 through E3 ubiquitin ligase parkin (PRKN). Blocking YAP degradation suppressed NDV-induced ferroptosis by suppressing the expression of Zrt/Irt-like protein 14 (ZIP14), a metal ion transporter that regulates iron uptake. These findings demonstrate that NDV exacerbated ferroptosis in tumor cells by inducing YAP degradation. Our study provides new insights into the mechanism of NDV-induced ferroptosis and highlights the critical role that oncolytic viruses play in the treatment of drug-resistant cancers.IMPORTANCEThe oncolytic Newcastle disease virus (NDV) is being developed for use in cancer treatment; however, its oncolytic mechanism is still not completely understood. The Hippo pathway, which is a tumor suppressor pathway, is frequently dysregulated in tumor tissues due to aberrant yes-associated protein 1 (YAP) activation. In this study, we have demonstrated that NDV degrades YAP to induce ferroptosis and promote virus replication in tumor cells. Notably, NDV was found to induce ubiquitin-mediated degradation of YAP at Lys90 through E3 ubiquitin ligase parkin (PRKN). Our study reveals a new mechanism by which NDV induces ferroptosis and provides new insights into NDV as an oncolytic agent for cancer treatment.

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.

Bovine parainfluenza type 3 virus induces incomplete autophagy to promote viral replication by activated beclin1 in vitro

Bovine Parainfluenza virus Type 3 (BPIV3) is one of the most important pathogens in cattle, capable of causing severe respiratory symptoms. Numerous studies have shown that autophagy plays a diverse role in the infection process of various pathogens. The influence of autophagy machinery on BPIV3 infection has not yet been confirmed. In the present study, we initially demonstrated that the expression of LC3 was significantly increased and exhibited a notable increase in double or single-membrane vesicles under a transmission electron microscope during BPIV3 infection. These observations unequivocally establish the induction of steady-state autophagy in vitro consequent to BPIV3 infection. Furthermore, quantification of autophagic flux substantiates the induction of an incomplete autophagic process during BPIV3 infection. Additionally, through targeted interventions, we demonstrate the regulatory impact of pharmacological agents influencing autophagy and RNA interference targeting an autophagy-associated protein on viral replication. Intriguingly, our data revealed that BPIV3 infection enhanced the phosphorylation of rapamycin kinase (mTOR). This result demonstrated that mTOR does not operate as a counteractive regulator of BPIV3-induced autophagy. Instead, we discern an augmentation in the expression of Beclin1, a key autophagy initiator, which complexes with Vps34, constituting a Class III phosphatidylinositol 3-kinase. This phenomenon serves as a hallmark in the inaugural phase of autophagy initiation during BPIV3 infection. Collectively, these discernments underscore that BPIV3 infection actively stimulates autophagy, thereby enhancing viral replication through the activation of Beclin1, independently of the mTOR signaling pathway. This nuanced comprehension significantly contributes to unraveling the intricate molecular mechanisms governing BPIV3-induced autophagy.

Newcastle disease virus infection remodels plasma phospholipid metabolism in chickens

Newcastle disease is a global problem that causes huge economic losses and threatens the health and welfare of poultry. Despite the knowledge gained on the metabolic impact of NDV on cells, the extent to which infection modifies the plasma metabolic network in chickens remains unknown. Herein, we performed targeted metabolomic and lipidomic to create a plasma metabolic network map during NDV infection. Meanwhile, we used single-cell RNA sequencing to explore the heterogeneity of lung tissue cells in response to NDV infection in vivo. The results showed that NDV remodeled the plasma phospholipid metabolism network. NDV preferentially targets infected blood endothelial cells, antigen-presenting cells, fibroblasts, and neutrophils in lung tissue. Importantly, NDV may directly regulate ribosome protein transcription to facilitate efficient viral protein translation. In conclusion, NDV infection remodels the plasma phospholipid metabolism network in chickens. This work provides valuable insights to further understand the pathogenesis of NDV.

Newcastle disease virus nucleocapsid protein mediates the degradation of 14-3-3ε to antagonize the interferon response and promote viral replication

Newcastle disease virus (NDV) is responsible for outbreaks that pose a threat to the global poultry industry. NDV triggers an interferon (IFN) response in the host upon infection. However, it also employs mechanisms that counteract this response. One important component in IFN-related signaling pathways is 14-3-3ε, which is known to interact with retinoic acid-inducible gene I (RIG-I) and mitochondrial antiviral signaling protein (MAVS). The relationship between 14 and 3-3ε and NDV infection has not been previously explored; therefore, this study aimed to investigate this relationship in vivo and in vitro using overexpressed and knockdown 14-3-3ε experiments, along with co-immunoprecipitation analysis. We found that NDV infection led to the degradation of 14-3-3ε. Furthermore, 14-3-3ε inhibited the replication of NDV, suggesting that NDV may enhance its own replication by promoting the degradation of 14-3-3ε during infection. The study revealed that 14-3-3ε is degraded by lysosomes and the viral protein nucleocapsid protein (NP) of NDV induces this degradation. It was also observed that 14-3-3ε is involved in activating the IFN pathway during NDV infection and mediates the binding of MDA5 to MAVS. Our study reveals that NDV NP mediates the entry of 14-3-3ε into lysosomes and facilitates its degradation. These findings contribute to the existing knowledge on the molecular mechanisms employed by NDV to counteract the IFN response and enhance its own replication.

The Viral Knock: Ameliorating Cancer Treatment with Oncolytic Newcastle Disease Virus

The prospect of cancer treatment has drastically transformed over the last four decades. The side effects caused by the traditional methods of cancer treatment like surgery, chemotherapy, and radiotherapy through the years highlight the prospect for a novel, complementary, and alternative cancer therapy. Oncolytic virotherapy is an evolving treatment modality that utilizes oncolytic viruses (OVs) to selectively attack cancer cells by direct lysis and can also elicit a strong anti-cancer immune response. Newcastle disease virus (NDV) provides a very high safety profile compared to other oncolytic viruses. Extensive research worldwide concentrates on experimenting with and better understanding the underlying mechanisms by which oncolytic NDV can be effectively applied to intercept cancer. This review encapsulates the potential of NDV to be explored as an oncolytic agent and discusses current preclinical and clinical research scenarios involving various NDV strains.

NDV-induced autophagy enhances inflammation through NLRP3/Caspase-1 inflammasomes and the p38/MAPK pathway

Newcastle disease (ND), caused by the Newcastle disease virus (NDV), is a highly virulent infectious disease of poultry. Virulent NDV can cause severe autophagy and inflammation in host cells. While studies have shown a mutual regulatory relationship between autophagy and inflammation, this relationship in NDV infection remains unclear. This study confirmed that NDV infection could trigger autophagy in DF-1 cells to promote cytopathic and viral replication. NDV-induced autophagy was positively correlated with the mRNA levels of inflammatory cytokines such as IL-1β, IL-8, IL-18, CCL-5, and TNF-α, suggesting that NDV-induced autophagy promotes the expression of inflammatory cytokines. Further investigation demonstrated that NLRP3 protein expression, Caspase-1 activity, and p38 phosphorylation level positively correlated with autophagy, suggesting that NDV-induced autophagy could promote the expression of inflammatory cytokines through NLRP3/Caspase-1 inflammasomes and p38/MAPK pathway. In addition, NDV infection also triggered mitochondrial damage and mitophagy in DF-1 cells, but did not result in a large leakage of reactive oxygen species (ROS) and mitochondrial DNA (mtDNA), indicating that mitochondrial damage and mitophagy do not contribute to the inflammation response during NDV infection.

Pathologic Mechanisms of the Newcastle Disease Virus

Newcastle disease (ND) has been a consistent risk factor to the poultry industry worldwide. Its pathogen, Newcastle disease virus (NDV), is also a promising antitumor treatment candidate. The pathogenic mechanism has intrigued the great curiosity of researchers, and advances in the last two decades have been summarized in this paper. The NDV’s pathogenic ability is highly related to the basic protein structure of the virus, which is described in the Introduction of this review. The overall clinical signs and recent findings pertaining to NDV-related lymph tissue damage are then described. Given the involvement of cytokines in the overall virulence of NDV, cytokines, particularly IL6 and IFN expressed during infection, are reviewed. On the other hand, the host also has its way of antagonizing the virus, which starts with the detection of the pathogen. Thus, advances in NDV’s physiological cell mechanism and the subsequent IFN response, autophagy, and apoptosis are summarized to provide a whole picture of the NDV infection process.

Canine distemper virus N protein induces autophagy to facilitate viral replication

BACKGROUND

Canine distemper virus (CDV) is one of the most contagious and lethal viruses known to the Canidae, with a very broad and expanding host range. Autophagy serves as a fundamental stabilizing response against pathogens, but some viruses have been able to evade or exploit it for their replication. However, the effect of autophagy mechanisms on CDV infection is still unclear.

RESULTS

In the present study, autophagy was induced in CDV-infected Vero cells as demonstrated by elevated LC3-II levels and aggregation of green fluorescent protein (GFP)-LC3 spots. Furthermore, CDV promoted the complete autophagic process, which could be determined by the degradation of p62, co-localization of LC3 with lysosomes, GFP degradation, and accumulation of LC3-II and p62 due to the lysosomal protease inhibitor E64d. In addition, the use of Rapamycin to promote autophagy promoted CDV replication, and the inhibition of autophagy by Wortmannin, Chloroquine and siRNA-ATG5 inhibited CDV replication, revealing that CDV-induced autophagy facilitated virus replication. We also found that UV-inactivated CDV still induced autophagy, and that nucleocapsid (N) protein was able to induce complete autophagy in an mTOR-dependent manner.

CONCLUSIONS

This study for the first time revealed that CDV N protein induced complete autophagy to facilitate viral replication.

β-catenin facilitates fowl adenovirus serotype 4 replication through enhancing virus-induced autophagy

β-catenin is a key component of the Wnt/β-catenin signal transduction cascade which is a highly conserved signaling pathway in eukaryotes. Increasing evidence suggests that the Wnt/β-catenin signaling pathway is involved in the infection of many viruses. However, its role in fowl adenovirus serotype 4 (FAdV-4) replication remains unclear. In the present study, we showed that FAdV-4 infection increased the expression of β-catenin and promoted the nuclear translocation of β-catenin. Overexpression of β-catenin and LiCl treatment stimulated the accumulation of β-catenin in the nucleus, and then facilitated FAdV-4 replication. Conversely, repression of β-catenin by inhibitors and siRNA significantly inhibited FAdV-4 replication. Furthermore, inhibition of autophagy by 3-Methyladenine (3-MA) suppressed the FAdV-4 replication, and repression of β-catenin inhibited the FAdV-4-triggered autophagy. In conclusion, the nuclear translocation of β-catenin benefits FAdV-4 replication, and suppression of β-catenin limits FAdV-4 production by inhibiting FAdV-4-induced autophagy. These findings indicated that β-catenin is an important regulator of FAdV-4 replication which can serve as a potential target for anti-FAdV-4 agents.

The DHAV-1 protein VP1 interacts with PI3KC3 to induce autophagy through the PI3KC3 complex

Duck hepatitis A virus type 1 (DHAV-1) is one of the main pathogens responsible for death in ducklings. Autophagy is a catabolic process that maintains cellular homeostasis, and the PI3KC3 protein plays an important role in the initiation of autophagy. DHAV-1 infection induces autophagy in duck embryo fibroblasts (DEFs) but the molecular mechanism between it and autophagy has not been reported. First, we determined that DHAV-1 infection induces autophagy in DEFs and that autophagy induction is dependent on the integrity of viral proteins by infecting DEFs with UV-inactivated or heat-inactivated DHAV-1. Then, in experiments using the pharmacological autophagy inducer rapamycin and the autophagy inhibitor chloroquine, autophagy inhibition was shown to reduce intracellular and extracellular DHAV-1 genome copies and viral titres. These results suggest that autophagy activated by DHAV-1 infection in DEFs affects DHAV-1 proliferation and extracellular release. Next, we screened the autophagy-inducing effects of the DHAV-1 structural proteins VP0, VP3, and VP1 and found that all DHAV-1 structural proteins could induce autophagy in DEFs but not the full autophagic flux. Finally, we found that VP1 promotes protein expression of PI3KC3 and Beclin1 by western blot experiments and that VP1 interacts with PI3KC3 by co-immunoprecipitation experiments; moreover, 3-MA-induced knockdown of PI3KC3 inhibited VP1 protein-induced autophagy in DEFs. In conclusion, the DHAV-1 structural protein VP1 regulates the PI3KC3 complex by interacting with PI3KC3 to induce autophagy in DEFs.

Inhibition of Porcine Epidemic Diarrhea Virus by Cinchonine via Inducing Cellular Autophagy

Porcine epidemic diarrhea virus (PEDV) could cause lethal diarrhea and dehydration in suckling piglets, which can adversely affect the development of the global swine industry. The lack of effective therapeutical and prophylactic treatment especially for PEDV variant strains underlines the importance of effective antiviral strategies, such as identification of novel antiviral agents. In the present study, the antiviral activity of cinchonine against PEDV was investigated in Vero CCL81 and LLC-PK1 cells at a non-cytotoxic concentration determined by Cell Counting Kit-8 assay in vitro. We found that cinchonine exhibited a significant suppression effect against PEDV infection and its inhibitory action was primarily focused on the early stage of PEDV replication. Moreover, we also observed that cinchonine could significantly induce autophagy by detecting the conversion of LC3-I to LC3-II by using western blot analysis. Cinchonine treatment could inhibit PEDV replication in a dose-dependent manner in Vero CCL81 cells, while this phenomenon disappeared when autophagy was attenuated by pre-treatment with autophagy inhibitor 3MA. Consequently, this study indicated that cinchonine can inhibit PEDV replication via inducing cellular autophagy and thus from the basis for successful antiviral strategies which potentially suggest the possibility of exploiting cinchonine as a novel antiviral agent.

Autophagy modulation in rainbow trout Oncorhynchus mykiss L. and resistance to experimental infection with Flavobacterium psychrophilum

Previously, rainbow trout fed deoxynivalenol (DON) or partially fed (pair-fed) for 4 weeks before and during experimental infection with Flavobacterium psychrophilum had significantly decreased mortality rates. Similar results were obtained in the present study after 12 days, but not after 6 days, feeding 5 ppm DON or pair-fed before infection. Furthermore, feeding 250 ppm chloroquine (CQ) also reduced mortality (p = .052) compared with controls and may have promise for treatment of some fish disease. Parallel groups of fish were maintained on the respective treatments for 15 days, with an additional group that was fasted, but were not infected to monitor autophagy. Fish that were fasted or fed DON had significantly increased LC3II in the liver and fasted fish had significantly decreased LC3II in muscle compared with controls using western blot. There was no difference in LC3II signal in the spleen of any treatment group. Fish that were fasted or pair-fed had significant up-regulation of the Atg genes atg4, atg7, lc3, gabarap and atg12 in muscle using quantitative PCR. Less alteration of Atg expression was seen in liver. Fish treated with CQ had significantly increased expression of atg4, becn1, lc3 and atg12 in the liver. Fish fed DON for 15 days had few alterations of Atg genes in either the liver or muscle. It is still not clear if autophagy is responsible for the resistance of rainbow trout fed DON, CQ or pair-fed before F. psychrophilum infection.

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.

Mitochondrial Dysfunction in Rabies Virus-Infected Human and Canine Brains

Rabies is a fatal encephalitis caused by the Rabies lyssavirus (RABV). The presence of minimal neuropathological changes observed in rabies indicates that neuronal dysfunction, rather than neuronal death contributes to the fatal outcome. The role of mitochondrial changes has been suggested as a possible mechanism for neuronal dysfunction in rabies. However, these findings are mostly based on studies that have employed experimental models and laboratory-adapted virus. Studies on brain tissues from naturally infected human and animal hosts are lacking. The current study investigated the role of mitochondrial changes in rabies by morphological, biochemical and proteomic analysis of RABV-infected human and canine brains. Morphological analysis showed minimal inflammation with preserved neuronal and disrupted mitochondrial structure in both human and canine brains. Proteomic analysis revealed involvement of mitochondrial processes (oxidative phosphorylation, cristae formation, homeostasis and transport), synaptic proteins and autophagic pathways, with over-expression of subunits of mitochondrial respiratory complexes. Consistent with these findings, human and canine brains displayed elevated activities of complexes I (p < 0.05), IV (p < 0.05) and V (p < 0.05). However, this did not result in elevated ATP production (p < 0.0001), probably due to lowered mitochondrial membrane potential as noted in RABV-infected cells in culture. These could lead to mitochondrial dysfunction and mitophagy as indicated by expression of FKBP8 (p < 0.05) and PINK1 (p < 0.001)/PARKIN (p > 0.05) and ensuing autophagy, as shown by the status of LCIII (p < 0.05), LAMP1 (p < 0.001) and pertinent ultrastructural markers. We propose that altered mitochondrial bioenergetics and cristae architecture probably induce mitophagy, leading to autophagy and consequent neuronal dysfunction in rabies.

Evasion of Host Antiviral Innate Immunity by Paramyxovirus Accessory Proteins

For efficient replication, viruses have developed multiple strategies to evade host antiviral innate immunity. Paramyxoviruses are a large family of enveloped RNA viruses that comprises diverse human and animal pathogens which jeopardize global public health and the economy. The accessory proteins expressed from the P gene by RNA editing or overlapping open reading frames (ORFs) are major viral immune evasion factors antagonizing type I interferon (IFN-I) production and other antiviral innate immune responses. However, the antagonistic mechanisms against antiviral innate immunity by accessory proteins differ among viruses. Here, we summarize the current understandings of immune evasion mechanisms by paramyxovirus accessory proteins, specifically how accessory proteins directly or indirectly target the adaptors in the antiviral innate immune signaling pathway to facilitate virus replication. Additionally, some cellular responses, which are also involved in viral replication, will be briefly summarized.

A Comprehensive View on the Host Factors and Viral Proteins Associated With Porcine Epidemic Diarrhea Virus Infection

Porcine epidemic diarrhea virus (PEDV), a coronavirus pathogen of the pig intestinal tract, can cause fatal watery diarrhea in piglets, thereby causing huge economic losses to swine industries around the world. The pathogenesis of PEDV has intensively been studied; however, the viral proteins of PEDV and the host factors in target cells, as well as their interactions, which are the foundation of the molecular mechanisms of viral infection, remain to be summarized and updated. PEDV has multiple important structural and functional proteins, which play various roles in the process of virus infection. Among them, the S and N proteins play vital roles in biological processes related to PEDV survival via interacting with the host cell proteins. Meanwhile, a number of host factors including receptors are required for the infection of PEDV via interacting with the viral proteins, thereby affecting the reproduction of PEDV and contributing to its life cycle. In this review, we provide an updated understanding of viral proteins and host factors, as well as their interactions in terms of PEDV infection. Additionally, the effects of cellular factors, events, and signaling pathways on PEDV infection are also discussed. Thus, these comprehensive and profound insights should facilitate for the further investigations, control, and prevention of PEDV infection.

Newcastle disease virus degrades SIRT3 via PINK1-PRKN-dependent mitophagy to reprogram energy metabolism in infected cells

Lacking a self-contained metabolism network, viruses have evolved multiple mechanisms for rewiring the metabolic system of their host to hijack the host's metabolic resources for replication. Newcastle disease virus (NDV) is a paramyxovirus, as an oncolytic virus currently being developed for cancer treatment. However, how NDV alters cellular metabolism is still far from fully understood. In this study, we show that NDV infection reprograms cell metabolism by increasing glucose utilization in the glycolytic pathway. Mechanistically, NDV induces mitochondrial damage, elevated mitochondrial reactive oxygen species (mROS) and ETC dysfunction. Infection of cells depletes nucleotide triphosphate levels, resulting in elevated AMP:ATP ratios, AMP-activated protein kinase (AMPK) phosphorylation, and MTOR crosstalk mediated autophagy. In a time-dependent manner, NDV shifts the balance of mitochondrial dynamics from fusion to fission. Subsequently, PINK1-PRKN-dependent mitophagy was activated, forming a ubiquitin chain with MFN2 (mitofusin 2), and molecular receptor SQSTM1/p62 recognized damaged mitochondria. We also found that NDV infection induces NAD⁺-dependent deacetylase SIRT3 loss via mitophagy to engender HIF1A stabilization, leading to the switch from oxidative phosphorylation (OXPHOS) to aerobic glycolysis. Overall, these studies support a model that NDV modulates host cell metabolism through PINK1-PRKN-dependent mitophagy for degrading SIRT3.Abbreviations: AMPK: AMP-activated protein kinase; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; ECAR: extracellular acidification rate; hpi: hours post infection LC-MS: liquid chromatography-mass spectrometry; mito-QC: mCherry-GFP-FIS1[mt101-152]; MFN2: mitofusin 2; MMP: mitochondrial membrane potential; mROS: mitochondrial reactive oxygen species; MOI: multiplicity of infection; 2-NBDG: 2-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino)-2-deoxyglucose; NDV: newcastle disease virus; OCR: oxygen consumption rate; siRNA: small interfering RNA; SIRT3: sirtuin 3; TCA: tricarboxylic acid; TCID₅₀: tissue culture infective doses.

Indicators of the molecular pathogenesis of virulent Newcastle disease virus in chickens revealed by transcriptomic profiling of spleen

Newcastle disease virus (NDV) has caused significant outbreaks in South-East Asia, particularly in Indonesia in recent years. Recently emerged genotype VII NDVs (NDV-GVII) have shifted their tropism from gastrointestinal/respiratory tropism to a lymphotropic virus, invading lymphoid organs including spleen and bursa of Fabricius to cause profound lymphoid depletion. In this study, we aimed to identify candidate genes and biological pathways that contribute to the disease caused by this velogenic NDV-GVII. A transcriptomic analysis based on RNA-Seq of spleen was performed in chickens challenged with NDV-GVII and a control group. In total, 6361 genes were differentially expressed that included 3506 up-regulated genes and 2855 down-regulated genes. Real-Time PCR of ten selected genes validated the RNA-Seq results as the correlation between them is 0.98. Functional and network analysis of Differentially Expressed Genes (DEGs) showed altered regulation of ElF2 signalling, mTOR signalling, proliferation of cells of the lymphoid system, signalling by Rho family GTPases and synaptogenesis signalling in spleen. We have also identified modified expression of IFIT5, PI3K, AGT and PLP1 genes in NDV-GVII infected chickens. Our findings in activation of autophagy-mediated cell death, lymphotropic and synaptogenesis signalling pathways provide new insights into the molecular pathogenesis of this newly emerged NDV-GVII.

Autophagy in farm animals: current knowledge and future challenges

Autophagy (a process of cellular self-eating) is a conserved cellular degradative process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Surprisingly, little attention has been paid to the role of this cellular function in species of agronomical interest, and the details of how autophagy functions in the development of phenotypes of agricultural interest remain largely unexplored. Here, we first provide a brief description of the main mechanisms involved in autophagy, then review our current knowledge regarding autophagy in species of agronomical interest, with particular attention to physiological functions supporting livestock animal production, and finally assess the potential of translating the acquired knowledge to improve animal development, growth and health in the context of growing social, economic and environmental challenges for agriculture.Abbreviations: AKT: AKT serine/threonine kinase; AMPK: AMP-activated protein kinase; ASC: adipose-derived stem cells; ATG: autophagy-related; BECN1: beclin 1; BNIP3: BCL2 interacting protein 3; BVDV: bovine viral diarrhea virus; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CMA: chaperone-mediated autophagy; CTSB: cathepsin B; CTSD: cathepsin D; DAP: Death-Associated Protein; ER: endoplasmic reticulum; GFP: green fluorescent protein; Gln: Glutamine; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; IF: immunofluorescence; IVP: in vitro produced; LAMP2A: lysosomal associated membrane protein 2A; LMS: lysosomal membrane stability; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MDBK: Madin-Darby bovine kidney; MSC: mesenchymal stem cells; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; NBR1: NBR1 autophagy cargo receptor; NDV: Newcastle disease virus; NECTIN4: nectin cell adhesion molecule 4; NOD1: nucleotide-binding oligomerization domain 1; OCD: osteochondritis dissecans; OEC: oviduct epithelial cells; OPTN: optineurin; PI3K: phosphoinositide-3-kinase; PPRV: peste des petits ruminants virus; RHDV: rabbit hemorrhagic disease virus; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy.

NDV related exosomes enhance NDV replication through exporting NLRX1 mRNA

Virulent Newcastle disease virus (NDV) is a violent infection in avian species. The understanding of its pathogenic mechanism is consistently evolving along with the development of molecular biological advancement. Exosomes derived from NDV infected cells (NDV Ex) were reported to promote virus replication through transportation of viral proteins and miRNAs. However, the function of mRNAs in NDV Ex remains unknown. In this study, a novel mechanism of NDV Ex to facilitate NDV infection was explored. Through transcriptome analysis, seven immune related genes were found to up-regulate in NDV Ex. Among them, NLRX1 mRNA was notably enriched in NDV Ex, and decreased inside the cells after virulent NDV infection. Further investigation suggested that NLRX1 mRNA decrease was in accordance with the NLRX1 protein expression reduction. This process can be reversed by the inhibition of exosome release. Therefore, NDV infection could utilize NDV Ex to export NLRX1 mRNA and reduce cellular NLRX1 protein. As NLRX1 is a crucial anti-viral protein of MAVS signal pathway, and NDV Ex transported NLRX1 cannot counteract its function in recipient cells, it can be concluded that NDV could benefit its replication through exporting NLRX1 mRNA to relieve the anti-viral pressure on its survival.

Caspase-Dependent Cleavage of DDX21 Suppresses Host Innate Immunity

DEAD (Glu-Asp-Ala-Glu) box RNA helicases have been proven to contribute to antiviral innate immunity. The DDX21 RNA helicase was identified as a nuclear protein involved in rRNA processing and RNA unwinding. DDX21 was also proven to be the scaffold protein in the complex of DDX1-DDX21-DHX36, which senses double-strand RNA and initiates downstream innate immunity. Here, we identified that DDX21 undergoes caspase-dependent cleavage after virus infection and treatment with RNA/DNA ligands, especially for RNA virus and ligands. Caspase-3/6 cleaves DDX21 at D126 and promotes its translocation from the nucleus to the cytoplasm in response to virus infection. The cytoplasmic cleaved DDX21 negatively regulates the interferon beta (IFN-β) signaling pathway by suppressing the formation of the DDX1-DDX21-DHX36 complex. Thus, our data identify DDX21 as a regulator of immune balance and most importantly uncover a potential role of DDX21 cleavage in the innate immune response to virus.

Antemortem inhibition of phosphoinositide 3-kinase causes changes in meat quality traits in broiler chickens

Phosphoinositide 3-kinase (PI3K) is an enzyme that mediates endocrinological responses, such as intracellular signaling of insulin and growth factors, and plays important roles in muscle homeostasis and growth. In this study, the effect of antemortem PI3K activity on meat quality traits was investigated using broiler chickens whose PI3K was inhibited pharmacologically. Breast and thigh muscles were harvested from broilers treated with the PI3K inhibitor wortmannin, and meat quality traits were evaluated by determination of color, water-holding capacity, and breaking strength. The pH and concentrations of glycogen and free amino acids were also investigated as determinants of the chemical properties of meat. The results indicated that antemortem PI3K inhibition by wortmannin modified breast muscle color with lower L∗ values (P < 0.05) and b∗ values (P < 0.05) and higher a∗ values (P < 0.05). Antemortem PI3K inhibition also increased the water-holding capacity of breast muscles (P < 0.05), although breaking strength was not much affected. In addition, antemortem PI3K inhibition increased the concentrations of free amino acids in breast muscles, especially arginine (P < 0.05) and glutamic acid (P < 0.05). Similar effects were observed in thigh muscles. Lower glycogen levels at sacrifice (P < 0.05) and the resultant higher pH during the postmortem period (P < 0.05) were associated with PI3K inhibition-induced changes in meat quality traits. The wortmannin-treated muscles shared certain features with dark, firm, and dry meat which is a common abnormal meat. These findings suggest that antemortem PI3K activity contributes to meat quality traits and is involved in the molecular mechanism of the production of meat quality abnormalities.

Autophagy in Viral Development and Progression of Cancer

Autophagy is a complex degradative process by which eukaryotic cells capture cytoplasmic components for subsequent degradation through lysosomal hydrolases. Although this catabolic process can be triggered by a great variety of stimuli, action in cells varies according to cellular context. Autophagy has been previously linked to disease development modulation, including cancer. Autophagy helps suppress cancer cell advancement in tumor transformation early stages, while promoting proliferation and metastasis in advanced settings. Oncoviruses are a particular type of virus that directly contribute to cell transformation and tumor development. Extensive molecular studies have revealed complex ways in which autophagy can suppress or improve oncovirus fitness while still regulating viral replication and determining host cell fate. This review includes recent advances in autophagic cellular function and emphasizes its antagonistic role in cancer cells.

Autophagy in Viral Development and Progression of Cancer

Autophagy is a complex degradative process by which eukaryotic cells capture cytoplasmic components for subsequent degradation through lysosomal hydrolases. Although this catabolic process can be triggered by a great variety of stimuli, action in cells varies according to cellular context. Autophagy has been previously linked to disease development modulation, including cancer. Autophagy helps suppress cancer cell advancement in tumor transformation early stages, while promoting proliferation and metastasis in advanced settings. Oncoviruses are a particular type of virus that directly contribute to cell transformation and tumor development. Extensive molecular studies have revealed complex ways in which autophagy can suppress or improve oncovirus fitness while still regulating viral replication and determining host cell fate. This review includes recent advances in autophagic cellular function and emphasizes its antagonistic role in cancer cells.

Impact of feed restriction, chloroquine and deoxynivalenol on viral haemorrhagic septicaemia virus IVb in fathead minnow Pimephales promelas Rafinesque

Autophagy can markedly alter host response to infectious disease, and several studies have demonstrated that a restricted diet or deoxynivalenol modulates autophagy and reduces mortality of fish due to bacterial disease. The picture is less clear for viral diseases of fish. Duplicate tanks of fathead minnow, Pimephales promelas Rafinesque, were fed a replete diet (control), 100 µM chloroquine, 5 µM deoxynivalenol, 10% (fasted) or 40% of a replete diet (pair-fed) for 2 weeks and then experimentally infected by intraperitoneal injection with 2 × 10⁵ viral haemorrhagic septicaemia virus IVb. Survival from highest to lowest for the different treatments was as follows: deoxynivalenol (average 43.3%); control (40.0%); pair-fed (35.0%); fasted (33.3%); and chloroquine (21.7%). No treatment significantly altered the survival rate of fathead minnow after VHSV IVb infection when compared to controls; however, the fish fed with chloroquine had significantly lower survival rate than the fish fed deoxynivalenol (p < .05).

Characterization of nucleocapsid and matrix proteins of Newcastle disease virus in yeast

Newcastle disease virus is a member of family Paramyxoviridae that infects chicken. Its genome comprises ~15.2 kb negative-sense RNA that encodes six major proteins. The virus encodes various proteins; among all, nucleocapsid (NP) and matrix (M) help in virus replication and its budding from the host cells, respectively. In this study, we investigated the intracellular distribution of NP and M upon expression in the yeast Saccharomyces cerevisiae. We observed nuclear targeting of M, and vacuolar localization of NP was observed in a fraction of yeast cells. Prolonged expression of GFP fused NP or M resulted in altered cell viability and intracellular production of reactive oxygen species in yeast cells. The expression of viral proteins did not alter the morphology and number of the organelles such as nucleus, mitochondria, endoplasmic reticulum, and peroxisomes. However, a significant effect was observed on vacuolar morphology and number in yeast cells. These observations point towards the importance of host cellular reorganization in viral infection. These findings may enable us to understand the conserved pathways affected in eukaryotic cells as a result of viral protein expression.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02624-4.

Activation of the extracellular signal-regulated kinase pathway is required for replication of Newcastle disease virus

Replication of Newcastle disease virus (NDV) is regulated by various host mechanisms, but the role of the extracellular signal-regulated kinase (ERK) pathway in regulating NDV replication is an open question. In this study, the relationship between the ERK pathway and NDV replication was investigated. NDV activated the ERK signaling in chicken embryo fibroblasts at the late stage of infection, correlating to expression of viral proteins. Specific blockage of the ERK pathway activation significantly decreased the transcription and translation levels of viral genes as well as virus replication and the cytopathogenic effect caused by NDV. Our results demonstrate that activation of the ERK pathway is required for NDV replication.

Identification and characterization of miRNA expression profiles across five tissues in giant panda

microRNA (miRNA) is a small endogenous noncoding RNA molecule that plays multiple roles in regulating most biological processes. However, for China's national treasure giant panda, a world-famous rare and protected species, reports of its miRNA have been found only in blood and breast milk. To explore the miRNA expression differences between different giant panda tissues, here, we generated the miRNA profiles of five tissues (heart, liver, spleen, lung, and kidney) from four giant pandas with Illumina Hiseq 2500 platform, and filtered the differentially expressed miRNAs (DEmiRs) in each tissue, predicted the target genes of miRNA from each tissue based on the DEmiRs. Then, the GO and KEGG enrichment analysis were conducted using the target genes predicted from DEmiRs in each tissue. The RNA-seq generated an average of 0.718 GB base per sample. A total of 1,256 known miRNAs and 12 novel miRNAs were identified, and there were 215, 131, 185, 83, and 126 tissue-specific DEmiRs filtered in the heart, liver, spleen, lung, and kidney, respectively, including miR-1b-5p, miR-122-5p, miR-143, miR-126-5p, and miR-10b-5p, respectively. The predicted target genes, including MYL2, LRP5, MIF, CFD, and PEBP1 in the heart, liver, spleen, lung, and kidney, respectively, were closely associated with tissue-specific biological functions. The enrichment analysis results of target genes showed tissue-specific characteristics, such as the significantly enriched GO terms extracellular matrix in the heart and insulin-like growth factor binding in the liver. The miRNA profiles of the heart, liver, spleen, lung, and kidney of giant panda have been reported in this study, it reveals the miRNA expression differences between different tissues of the giant panda, and provides valuable genetic resources for the further related molecular genetic research of the rare and protected species giant panda and other mammals.

VHSV IVb infection and autophagy modulation in the rainbow trout gill epithelial cell line RTgill-W1

Autophagy modulation influences the success of intracellular pathogens, and an understanding of the mechanisms involved might offer practical options to reduce the impact of infectious disease. Viral haemorrhagic septicaemia virus (VHSV) can cause high mortality and economic loss in some commercial fish species. VHSV IVb was used to infect a rainbow trout gill cell line, RTgill-W1, followed by the treatment of the cells with different autophagy-modulating reagents. LC3II protein using Western blot was significantly (p < .05) decreased for two days following VHSV infection, and immunofluorescence confirmed that LC3II-positive intracytoplasmic puncta were also decreased. Infection with VHSV resulted in significantly decreased expression of the autophagy-related (Atg) genes atg4, at12, atg13 and becn1 after one day using quantitative PCR. Both viral gene copy number and VHSV N protein were significantly decreased by treating the cells with autophagy-blocking (chloroquine) and autophagy-inhibiting reagents (deoxynivalenol and 3-methyladenine) after three days, while autophagy induction (restricted nutrition and rapamycin) had limited effect. Only treatment of RTgill-W1 with deoxynivalenol resulted in a significant increase in expression of type I interferon. Therefore, the suppression of autophagy initially occurs after VHSV IVb infection, but the modulation of autophagy can also inhibit VHSV IVb infection in RTgill-W1 after three days.

Eating the unknown: Xenophagy and ER-phagy are cytoprotective defenses against pathogens

Autophagy is an evolutionary conserved catabolic process devoted to the removal of unnecessary and harmful cellular components. In its general form, autophagy governs cellular lifecycle through the formation of double membrane vesicles, termed autophagosomes, that enwrap and deliver unwanted intracellular components to lysosomes. In addition to this omniscient role, forms of selective autophagy, relying on specialized receptors for cargo recognition, exert fine-tuned control over cellular homeostasis. In this regard, xenophagy plays a pivotal role in restricting the replication of intracellular pathogens, thus acting as an ancient innate defense system against infections. Recently, selective autophagy of the endoplasmic reticulum (ER), more simply ER-phagy, has been uncovered as a critical mechanism governing ER network shape and function. Six ER-resident proteins have been characterized as ER-phagy receptors and their orchestrated function enables ER homeostasis and turnover overtime. Unfortunately, ER is also the preferred site for viral replication and several viruses hijack ER machinery for their needs. Thus, it is not surprising that some ER-phagy receptors can act to counteract viral replication and minimize the spread of infection throughout the organism. On the other hand, evolutionary pressure has armed pathogens with strategies to evade and subvert xenophagy and ER-phagy. Although ER-phagy biology is still in its infancy, the present review aims to summarize recent ER-phagy literature, with a special focus on its role in counteracting viral infections. Moreover, we aim to offer some hints for future targeted approaches to counteract host-pathogen interactions by modulating xenophagy and ER-phagy pathways.

Pharmacological and nutritional modulation of autophagy in a rainbow trout (Oncorhynchus mykiss) gill cell line, RTgill-W1

Autophagy is involved in the modulation of nutrition, immunity, and disease in humans and animals. To understand the impact of autophagy modulation on a rainbow trout gill cell line, RTgill-W1, treatments including reduced nutrition (2% fetal bovine serum compared with 10% control), rapamycin, 3-methyladenine, deoxynivalenol, and chloroquine were tested. Western blot and immunofluorescence were used to detect microtubule-associated protein 1A/1B-light chain protein and quantitative polymerase chain reaction was used to detect the expression of 10 autophagy-related genes. At 3-d post-treatment, reduced nutrition significantly (p < 0.05) increased autophagy while deoxynivalenol significantly (p < 0.01) suppressed it compared to controls. These phenomena were confirmed by using immunofluorescence to detect the number of autophagosomes in RTgill-W1. Chloroquine is critical to allow observation of microtubule-associated protein 1A/1B-light chain protein in this model. The commonly used autophagy-modulating chemicals rapamycin and 3-methyladenine either activated or suppressed microtubule-associated protein 1A/1B-light chain protein, respectively, as expected from the literature, but did not act in a consistently significant manner. Expression of five of the 10 Atg genes, including lc3, gabarap, atg4, atg7, and atg12, were altered in a similar pattern to microtubule-associated protein 1A/1B-light chain protein. The consistent trend of autophagy-related gene upregulation including becn1, lc3, gabarap, and atg9 following treatment with 3-methyladenine and chloroquine is suggestive of a novel feedback regulation in the autophagy machinery.

Oncolytic effects of Hitchner B1 strain of newcastle disease virus against cervical cancer cell proliferation is mediated by the increased expression of cytochrome C, autophagy and apoptotic pathways

Newcastle disease virus (NDV) is a potential oncolytic virus for the cancer treatment due to its ability to replicate in tumor cells. The aim of this study was to evaluate the in vitro anticancer properties of Hitchner B1 (HB1) strain of NDV on TC-1 cell line and underlying molecular mechanisms. The cytolytic effects of oncolytic HB1 strain of NDV was determined by lactate dehydrogenase (LDH) release assay. Apoptosis, intracellular reactive oxygen species (ROS) levels, cleaved caspase-3 and autophagy were evaluated by flow cytometry. Cytochrome-C and survivin protein levels were distinguished by Enzyme-Linked Immunosorbent Assay (ELISA). Our results from LDH method showed that the viability of the TC-1 cell line following HB1 NDV infection was dose-dependent and decreased significantly with increasing the dose of HB1 NDV infection (MOIs: 5, 10, and 15). Other evaluations also revealed that HB1 strain of NDV potentially led to the ROS production, and apoptosis and autophagy induction in TC-1 cell line in a dose-dependent manner. The in vitro experiments also presented that NDV treatment significantly up-regulated the expression of cytochrome-C and down-regulated the expression of survivin, as detected by ELISA assay. Our results confirmed that the HB1 NDV could be introduced as a powerful candidate for the therapy of cervical cancer. However, further examinations are needed to explain the underlying mechanisms of the HB1 NDV against TC-1 cell line and cervical cancer.

Siniperca chuatsi rhabdovirus (SCRV) induces autophagy via PI3K/Akt-mTOR pathway in CPB cells

Autophagy is an important mechanism for organisms to eliminate viruses and other intracellular pathogens. Siniperca chuatsi rhabdovirus (SCRV) is an agent that has caused devastating losses in Chinese perch (Siniperca chuatsi) industry. But the role of autophagy in Siniperca chuatsi rhabdovirus (SCRV) infection is not clearly understood. In this study, we identified that SCRV infection triggered autophagy in CPB cells, which was demonstrated by the appearance of the membrane vesicles, GFP-LC3 punctuate pattern, conversion of LC3-I to LC3-II, and the co-localization of autophagosomes and lysosomes. The changes of autophagy flux in SCRV infection indicated that autophagy was inhibited at the early stage of SCRV infection, but was promoted at the late stage. UV-inactivated SCRV can induce autophagy, suggesting that SCRV replication is not essential for the induction of autophagy. Furthermore, we found inducing autophagy with Rapa inhibited SCRV proliferation, but inhibiting autophagy with 3-MA or CQ increased SCRV production in CPB cells. Then we assessed the effects of PI3K/Akt-mTOR signaling pathway on SCRV induced autophagy. We found that SCRV infection activated PI3K/AKT signaling pathway at 4 hpi, but inhibited it at 8 hpi. SCRV-N mRNA and protein level were decreased by inhibiting PI3K with LY294002, but increased by activating PI3K with 740Y-P. Those results indicated that SCRV infection induced autophagy via the PI3K/Akt-mTOR signal pathway, which will provide new insights into SCRV pathogenesis and antiviral treatment strategies.

Newcastle Disease virus infection activates PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways to benefit viral mRNA translation via interaction of the viral NP protein and host eIF4E

Newcastle disease virus (NDV), a member of the Paramyxoviridae family, can activate PKR/eIF2α signaling cascade to shutoff host and facilitate viral mRNA translation during infection, however, the mechanism remains unclear. In this study, we revealed that NDV infection up-regulated host cap-dependent translation machinery by activating PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways. In addition, NDV infection induced p38 MAPK/Mnk1 signaling participated 4E-BP1 hyperphosphorylation for efficient viral protein synthesis when mTOR signaling is inhibited. Furthermore, NDV NP protein was found to be important for selective cap-dependent translation of viral mRNAs through binding to eIF4E during NDV infection. Taken together, NDV infection activated multiple signaling pathways for selective viral protein synthesis in infected cells, via interaction between viral NP protein and host translation machinery. Our results may help to design novel targets for therapeutic intervention against NDV infection and to understand the NDV anti-oncolytic mechanism.

Viruses are obligate intracellular parasites and have no protein translation machinry of their own. Therefore, viruses remain exclusively dependent on host translation machinery to ensure viral protein synthesis and progeny virion production during infection. We previous reported that Newcastle disease virus (NDV) shutoff host and facilitate viral mRNA translation by activating PKR/eIF2α signaling cascade. Here, we demonstrated that NDV infection up-regulated host cap-dependent translation machinery by activating PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways. Furthermore, NDV NP protein was found to be important for selective cap-dependent translation of viral mRNAs. Our findings highlight a new strategy how virus used host translation machinery for selective viral protein synthesis.

Newcastle disease virus induces testicular damage and disrupts steroidogenesis in specific pathogen free roosters

Newcastle disease (ND), which is caused by Newcastle disease virus (NDV), can cause heavy economic losses to the poultry industry worldwide. It is characterised by extensive pathologies of the digestive, respiratory, and nervous systems and can cause severe damage to the reproductive system of egg-laying hens. However, it is unknown whether NDV replicates in the male reproductive system of chickens and induces any pathologies. In this study, we selected a representative strain (i.e. ZJ1) of the most common genotype (i.e. VII) of NDV to investigate whether NDV can induce histological, hormonal, and inflammatory responses in the testes of specific pathogen free (SPF) roosters. NDV infection increased the expression of toll like receptor TLR3, TLR7, MDA5, IFN-α, IFN-β, IFN-γ, IL-8, and CXCLi1 in the testes of NDV-infected roosters at 5 days post-infection (dpi). Severe histological changes, including decrease in the number of Sertoli cells and individualized, shrunken spermatogonia with pyknotic nuclei, were observed at 3 dpi. At 5 dpi, the spermatogenic columns were disorganized, and there were fewer cells, which were replaced by necrotic cells, lipid vacuoles, and proteinaceous homogenous material. A significant decrease in the plasma concentrations of testosterone and luteinizing hormone (LH) and the mRNA expression of their receptors in the testes, steroidogenic acute regulatory protein, cytochrome P450 side-chain cleavage enzyme, and 3β-hydroxysteroid dehydrogenase in the NDV-infected group was observed relative to those in the control group (P < 0.05). Collectively, these results indicate that NDV infection induces a severe inflammatory response and histological changes, which decrease the steroidogenesis.

Cyclooxygenase-2 Facilitates Newcastle Disease Virus Proliferation and Is as a Target for Canthin-6-One Antiviral Activity

Cyclooxygenase-2 (COX-2), one of the mediators of inflammation in response to viral infection, plays an important role in host antiviral defense system. But its role in Newcastle disease virus (NDV) proliferation process remains unclear. This study revealed that inhibition of COX-2 could benefit NDV proliferation and overexpression of COX-2 dose-dependently suppressed NDV proliferation. Overexpression of COX-2 also showed inhibitory effect on NDV-induced endoplasmic reticulum (ER)-stress and autophagy, also promoted the expression of antiviral genes. However, prostaglandin E₂ (PGE₂), the major product of COX-2, had indistinctive effects on NDV proliferation. At variant time point post viral infection, a tight regulation pattern of COX-2 by NDV was observed. Using inhibitors and siRNA against signaling molecules, the nuclear factor-κB (NF-κB) and melanoma differentiation-associated gene 5 (MDA5) were identified as critical factors for NDV induced COX-2 expression. Nonetheless, at late stage of NDV proliferation, substantial suppression of COX-2 protein synthesis could be detected, accompanied by a decrease in mRNA half-life. Furthermore, three C ring-truncated canthin-6-one analogs were used to activate COX-2 expression and showed inhibitory effect on NDV proliferation with the effective concentrations on μM level. Taken together, these results illustrated a novel NDV-regulated cellular mechanism and indicated that COX-2 is an important regulator of NDV proliferation which can serve as a potential target for anti-NDV agents.

Manipulation of autophagy by (+) RNA viruses

Autophagy is an evolutionarily conserved process central to host metabolism. Among its major functions are conservation of energy during starvation, recycling organelles, and turnover of long-lived proteins. Besides, autophagy plays a critical role in removing intracellular pathogens and very likely represents a primordial intrinsic cellular defence mechanism. More recent findings indicate that it has not only retained its ability to degrade intracellular pathogens, but also functions to augment and fine tune antiviral immune responses. Interestingly, viruses have also co-evolved strategies to manipulate this pathway and use it to their advantage. Particularly intriguing is infection-dependent activation of autophagy with positive stranded (+)RNA virus infections, which benefit from the pathway without succumbing to lysosomal degradation. In this review we summarise recent data on viral manipulation of autophagy, with a particular emphasis on +RNA viruses and highlight key unanswered questions in the field that we believe merit further attention.

Quantitative Proteomics Analysis Revealed Compromised Chicken Dendritic Cells Function at Early Stage of Very Virulent Infectious Bursal Disease Virus Infection

Chicken dendritic cells (DCs) have been demonstrated to be susceptible to infectious bursal disease virus (IBDV), a causative agent of acute and immunosuppressed disease in young chicks known as infectious bursal disease. Further functional characterization of IBDV-infected DCs of chickens is required to provide a better understanding on the influence of the virus on chicken bone marrow-derived dendritic cells (BM-DCs) following very virulent (vv) IBDV infection. Membrane proteins of BM-DCs were extracted and the proteins were further denatured and reduced before performing labeling with isobaric tags for relative and absolute quantitation. The differential expression protein profiles were identified and quantified using liquid chromatography coupled with tandem mass spectrometry, and later validated using flow cytometry and real-time reverse transcriptase PCR. The analysis has identified 134 differentially regulated proteins from a total of 283 proteins (cutoff values of ≤0.67, ≥1.5, and ProtScore >1.3 at 95% confidence interval), which produced high-yield membrane fractions. The entry of vvIBDV into the plasma membrane of BM-DCs was observed at 3 hr postinfection by the disruption of several important protein molecule functions, namely apoptosis, RNA/DNA/protein synthesis, and transport and cellular organization, without the activation of proteins associated with signaling. At the later stage of infection, vvIBDV induced expression of several proteins, namely CD200 receptor 1-A, integrin alpha-5, HSP-90, cathepsin, lysosomal-associated membrane protein, and Ras-related proteins, which play crucial roles in signaling, apoptosis, stress response, and antigen processing as well as in secretion of danger-associated proteins. These findings collectively indicated that the chicken DCs are expressing various receptors regarded as potential targets for pathogen interaction during viral infection. Therefore, fundamental study of the interaction of DCs and IBDV will provide valuable information in understanding the role of professional antigen-presenting cells in chickens and their molecular interactions during IBDV infection and vaccination.

Autophagy Is a Potential Therapeutic Target Against Duck Tembusu Virus Infection in vivo

Duck tembusu virus (DTMUV) is newly emerged in poultry and causes great losses to the breeding industry in China and neighboring countries. Effective antiviral strategies are still being studied. Autophagy is a cellular degradative pathway, and our lab's previous data show that autophagy promotes DTMUV replication in vitro. To study the role of autophagy further in vivo, we utilized ducks as the animal model to investigate the autophagy responses in DTMUV-targeted tissues. And also, we utilized autophagy regulators, including Rapamycin (Rapa) as the autophagy enhancer, 3-Methyladenine (3-MA) and Chloroquine (CQ) as the autophagy inhibitors, to adjust the host autophagic levels and then study the effects of autophagy on tissue damages and virus replication. As a result, we first found DTMUV infection trigged autophagy and autophagy regulator treatments regulated autophagy levels successfully in duck spleens and brains. Next, we found that autophagy inhibitors inhibited DTMUV replication and alleviated DTMUV-induced pathological symptoms, whereas the autophagy inducer treatment led to the opposite effects. And we also found that autophagic regulation was correlated with the expression of innate immune genes, including pattern recognition receptors, type I interferons, and cytokines, and caused different effects in different tissues. In summary, we demonstrated that autophagy facilitated DTMUV replication, aggravated the developments of pathological symptoms and possibly counteracts the host's innate immunity response in vivo.

Influenza A virus protein PB1-F2 impairs innate immunity by inducing mitophagy

Influenza A virus (IAV) infection induces mitophagy, which is essential for the clearance of damaged mitochondria. Dysfunctional mitochondria can be selectively targeted by PINK1, which recruits PRKN/PARK2 and leads to subsequent mitochondrial sequestration within autophagosomes. The IAV PB1-F2 protein translocates to mitochondria, accelerates the mitochondrial fragmentation and impairs the innate immunity. However, whether PB1-F2 mediates IAV-induced mitophagy and the relation between mitophagy and PB1-F2-attenuated innate immunity remain obscure. Here, we showed that PB1-F2 translocated to mitochondria by interacting and colocalizing with TUFM (Tu translation elongation factor, mitochondrial). Further studies revealed that PB1-F2 induced complete mitophagy, which required the interactions of PB1-F2 with both TUFM and MAP1LC3B/LC3B that mediated the autophagosome formation. PB1-F2-induced mitophagy was critical for the MAVS (mitochondrial antiviral signaling protein) degradation and led to its suppression of the type I IFN production. Importantly, the C-terminal LIR motif of PB1-F2 protein was demonstrated to be essential for its mitophagy induction and attenuated innate immunity. In conclusion, PB1-F2-induced mitophagy strongly correlates with impaired cellular innate immunity, revealing it is a potential therapeutic target.Abbreviations: BCL2L13: BCL2 like 13; BECN1: beclin 1; BNIP3L/Nix: BCL2 interacting protein 3 like; CQ: chloroquine; DDX58: DExD/H-box helicase 58; eGFP: enhanced green fluorescent protein; hpi: hours post infection; IAV: influenza A virus; IFN: interferon; IP: immunoprecipitation; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAVS: mitochondrial antiviral signaling protein; MMP: mitochondrial membrane potential; MOI, multiplicity of infection; mRFP: monomeric red fluorescent protein; NBR1: NBR1 autophagy cargo receptor; NC: negative control; NLRP3: NLR family pyrin domain containing 3; PINK1: PTEN induced kinase 1; PRKN/PARK2: parkin RBR E3 ubiquitin protein ligase; RLR: RIG-I-like-receptor; ROS: reactive oxygen species; SEV: sendai virus; SQSTM1/p62: sequestosome 1; TAX1BP1: Tax1 binding protein 1; TM: transmembrane; TOMM20/40: translocase of outer mitochondrial membrane 20/40; TUFM: Tu translation elongation factor, mitochondrial.

The inhibitory effect of phosphorylated Codonopsis pilosula polysaccharide on autophagosomes formation contributes to the inhibition of duck hepatitis A virus replication

Duck hepatitis A virus type 1 (DHAV) infection causes duck viral hepatitis and results in enormous loss to poultry farming industry. We reported that phosphorylated Codonopsis pilosula polysaccharide (pCPPS) inhibited DHAV genome replication. Here we further explored its underlying antiviral mechanisms. Autophagosomes formation is essential for the genome replication of picornaviruses. In this study, Western blot, confocal microscopy observation, and ELISA methods were performed to analyze polysaccharides' effects on autophagy by the in vitro and in vivo experiments. Results obtained from in vitro and in vivo experiments showed that Codonopsis pilosula polysaccharide did not play a role in regulating autophagy and had no therapeutic effects on infected ducklings. However, pCPPS treatment downregulated LC3-II expression level activated by DHAV and rapamycin, indicating the inhibition of autophagosomes formation. The interdiction of autophagosomes formation resulted in the inhibition of DHAV genome replication. Further study showed that pCPPS treatment reduced the concentration of phosphatidylinositol-3-phosphate (PI3P), an important component of membrane, in cells and serum, and consequently, autophagosomes formation was downregulated. In vivo experiments also verified the therapeutic effect of pCPPS. Phosphorylated Codonopsis pilosula polysaccharide treatment increased the infected ducklings' survival rate and alleviated hepatic injury. Our studies verified the effects of pCPPS against DHAV infection in duck embryo hepatocytes and ducklings and confirmed that phosphorylated modification enhanced the bioactivities of polysaccharides. The results also stated pCPPS's antiviral mechanisms, provided fundamental basis for the development of new anti-DHAV agents.

Autophagy Promotes Duck Tembusu Virus Replication by Suppressing p62/SQSTM1-Mediated Innate Immune Responses In Vitro

Duck Tembusu virus (DTMUV) has recently appeared in ducks in China and the key cellular determiners for DTMUV replication in host cells remain unknown. Autophagy is an evolutionarily conserved cellular process that has been reported to facilitate flavivirus replication. In this study, we utilized primary duck embryo fibroblast (DEF) as the cell model and found that DTMUV infection triggered LC3-II increase and polyubiquitin-binding protein sequestosome 1 (p62) decrease, confirming that complete autophagy occurred in DEF cells. The induction of autophagy by pharmacological treatment increased DTMUV replication in DEF cells, whereas the inhibition of autophagy with pharmacological treatments or RNA interference decreased DTMUV replication. Inhibiting autophagy enhanced the activation of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and interferon regulatory factor 7 (IRF7) pathways and increased the p62 protein level in DTMUV-infected cells. We further found that the overexpression of p62 decreased DTMUV replication and inhibited the activation of the NF-κB and IRF7 pathways, and changes in the NF-κB and IRF7 pathways were consistent with the level of phosphorylated TANK-binding kinase 1 (p-TBK1). Opposite results were found in p62 knockdown cells. In summary, we found that autophagy-mediated p62 degradation acted as a new strategy for DTMUV to evade host innate immunity.

Establishment of canine macrophages stably expressing GFP-tagged canine LC3 protein for effectively detecting autophagy

Autophagy plays a crucial role in eliminating protein aggregates, damaged organelles and invading pathogens. Genetically engineered cell line stably expressing green fluorescent protein (GFP)-tagged microtubule-associated protein light chain 3 (LC3) is extensively used to test autophagy through observing GFP puncta formation in the cells by fluorescence imaging. However, canine LC3 (cLC3) gene has not been cloned, therefore, GFP-tagged canine LC3 (GFP-cLC3) detection system has not been established. To generate GFP-cLC3 stably expressing canine-derived macrophages, the cLC3 cDNA was first amplified by RT-PCR and inserted into pEGFP-C1 plasmid to create GFP-cLC3 gene fusion. This genetic element was then transducted into canine macrophages mediated by lentivirus vector to generate the canine macrophages stably expressing fusion protein. Results showed that the sequence of cLC3 cloned in this study is highly homologous with other animals (80-95% homology). Phenotypic and functional analysis of these engineered cells revealed that GFP-cLC3 was indeed stably expressed and rapamycin or starvation can effectively induce GFP puncta formation in the cells, indicative of autophagosome formation. These GFP-cLC3-expressing cells may thus be useful to study autophagy in canine.