Autophagy inhibitors reduce avian-reovirus-mediated apoptosis in cultured cells and in chicken embryos

Cholesterol 25-hydroxylase suppresses avian reovirus replication by its enzymatic product 25-hydroxycholesterol

Avian reovirus (ARV) causing viral arthritis/tenosynovitis and viral enteritis in domestic fowl has significantly threatened on the poultry industry worldwide. ARV is a non-enveloped fusogenic virus that belongs to the Reoviridae family. Previous research revealed that cellular cholesterol in lipid rafts is essential for ARV replication. It has been reported that cholesterol 25-hydroxylase (CH25H) and its product 25-hydroxycholesterol (25HC) have antiviral activities against enveloped viruses. However, few studies characterized the association of non-enveloped viruses with CH25H and the role of CH25H in the regulation of ARV replication. In this study, the expression of chicken CH25H (chCH25H) was found to be upregulated in ARV-infected cells at the early stage of infection. The results of overexpression and knockdown assays revealed that chCH25H has a significant antiviral effect against ARV infection. Furthermore, a 25HC treatment significantly inhibited ARV replication in a dose-dependent manner at both the entry and post-entry stages, and a chCH25H mutant lacking hydroxylase activity failed to inhibit ARV infection. These results indicate that CH25H, depending on its enzyme activity, exerts the antiviral effect against ARV via the synthesis of 25HC. In addition, we revealed that 25HC produced by CH25H inhibits viral entry by delaying the kinetics of ARV uncoating, and CH25H blocks cell-cell membrane fusion induced by the p10 protein of ARV. Altogether, our findings showed that CH25H, as a natural host restriction factor, possessed antiviral activity against ARV targeting viral entry and syncytium formation, through an enzyme activity-dependent way. This study may provide new insights into the development of broad-spectrum antiviral therapies.

Avian Reovirus σB Interacts with Caveolin-1 in Lipid Rafts during Dynamin-Dependent Caveolae-Mediated Endocytosis

Caveolin-1 (Cav-1) is the basic component of caveolae, a specialized form of lipid raft that plays an essential role in endocytic viral entry. However, the evidence of direct involvement of caveolae and Cav-1 in avian reovirus (ARV) entry remains insufficient. In this study, the membrane lipid rafts were isolated as detergent-resistant microdomains (DRMs) by sucrose gradient centrifugation, and the capsid protein σB of ARV was found to associate with Cav-1 in DRMs fractions. Additionally, the interaction between ARV σB protein and Cav-1 was demonstrated by immunofluorescence co-localization and co-immunoprecipitation assays. Furthermore, we found that the internalization of ARV is sensitive to caveolae and dynamin inhibitors, while it is insensitive to clathrin inhibitors. In conclusion, these results indicate that the ARV σB protein interacts with Cav-1 during dynamin-dependent caveolae-mediated endocytosis for the entry of ARV.

Gga-miR-30c-5p Suppresses Avian Reovirus (ARV) Replication by Inhibition of ARV-Induced Autophagy via Targeting ATG5

Avian reovirus (ARV) is an important poultry pathogen causing viral arthritis, chronic respiratory diseases, and retarded growth, leading to considerable economic losses to the poultry industry across the globe. Elucidation of the pathogenesis of ARV infection is crucial to guiding the development of novel vaccines or drugs for the effective control of these diseases.

Reovirus Activated Cell Death Pathways

Mammalian orthoreoviruses (ReoV) are non-enveloped viruses with segmented double-stranded RNA genomes. In humans, ReoV are generally considered non-pathogenic, although members of this family have been proven to cause mild gastroenteritis in young children and may contribute to the development of inflammatory conditions, including Celiac disease. Because of its low pathogenic potential and its ability to efficiently infect and kill transformed cells, the ReoV strain Type 3 Dearing (T3D) is clinical trials as an oncolytic agent. ReoV manifests its oncolytic effects in large part by infecting tumor cells and activating programmed cell death pathways (PCDs). It was previously believed that apoptosis was the dominant PCD pathway triggered by ReoV infection. However, new studies suggest that ReoV also activates other PCD pathways, such as autophagy, pyroptosis, and necroptosis. Necroptosis is a caspase-independent form of PCD reliant on receptor-interacting serine/threonine-protein kinase 3 (RIPK3) and its substrate, the pseudokinase mixed-lineage kinase domain-like protein (MLKL). As necroptosis is highly inflammatory, ReoV-induced necroptosis may contribute to the oncolytic potential of this virus, not only by promoting necrotic lysis of the infected cell, but also by inflaming the surrounding tumor microenvironment and provoking beneficial anti-tumor immune responses. In this review, we summarize our current understanding of the ReoV replication cycle, the known and potential mechanisms by which ReoV induces PCD, and discuss the consequences of non-apoptotic cell death—particularly necroptosis—to ReoV pathogenesis and oncolysis.

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.

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.

Cholesterol-Rich Lipid Rafts in the Cellular Membrane Play an Essential Role in Avian Reovirus Replication

Cholesterol is an essential component of lipid rafts in cellular plasma membranes. Although lipid rafts have been reported to have several functions in multiple stages of the life cycles of many different enveloped viruses, the mechanisms by which non-enveloped viruses, which lack outer lipid membranes, infect host cells remain unclear. In this study, to investigate the dependence of non-enveloped avian reovirus (ARV) infection on the integrity of cholesterol-rich membrane rafts, methyl-β-cyclodextrin (MβCD) was used to deplete cellular membrane cholesterol at the ARV attachment, entry, and post-entry stages. Treatment with MβCD significantly inhibited ARV replication at both the entry and post-entry stages in a dose-dependent manner, but MβCD had a statistically insignificant effect when it was added at the attachment stage. Moreover, MβCD treatment markedly reduced syncytium formation, which occurs at a relatively late stage of the ARV life cycle and is involved in cell-cell transmission and release. Furthermore, the addition of exogenous cholesterol reversed the effects mentioned above. Colocalization data also showed that the ARV proteins σC, μNS, and p10 prefer to localize to cholesterol-rich lipid raft regions during ARV infection. Altogether, these results suggest that cellular cholesterol in lipid rafts plays a critical role in ARV replication.

Autophagy induced by avian reovirus enhances viral replication in chickens at the early stage of infection

BACKGROUND

Avian reovirus (ARV) is an important pathogen that can cause serious disease in poultry. Though several in vitro studies revealed some molecular mechanisms that are responsible for ARV-induced autophagy, it is still largely unknown how ARV manipulates autophagy to promote its own propagation.

RESULTS

In this study, we demonstrated that ARV infection triggered autophagy in chicken tissues, evident from the enhancement of LC3-I/-II conversion and the appearance of abundant autophagosomes. Moreover, viral replication and the expression of IL-1β were coupled with the process of ARV-induced autophagy in the early stage of infection. Furthermore, regulation of autophagy affected the accumulation of LC3-II, the production of ARV and the expression of IL-1β.

CONCLUSIONS

Altogether, our data suggest that ARV induces autophagy, which benefits its replication and dissemination in chicken tissues at the early infection stage.

The protease inhibitor E64d improves ox-LDL-induced endothelial dysfunction in human aortic endothelial cells

Oxidized low-density lipoprotein (ox-LDL)-induced endothelial dysfunction in human vascular endothelial cells contributes to the development of atherosclerosis. E64d, a cysteine protease inhibitor, blocks the elastolytic activity of cathepsin essential for vascular matrix remodeling and reduces neurovascular endothelial apoptosis. The objective of this study was to investigate the effects and the underling mechanisms of E64d on ox-LDL-induced endothelial dysfunction in human aortic endothelial cells (HAECs). HAECs were treated with various concentrations of ox-LDL (0–200 mg/L) for 24 h with or without E64d. The results showed that E64d attenuated ox-LDL-induced increase in soluble intercellular adhesion molecule-1 (sICAM-1) concentration and reduction in endothelial nitric oxide synthase (eNOS) expression, prevented ox-LDL-induced reduction in cell viability and migration ability of HAECs. E64d decreased the protein expression of cathepsin B (CTSB), Beclin 1, and microtubule-associated protein light chain 3 (LC3)-II, but not p62. LC3 puncta and autophagosome formation were also reduced by E64d in HAECs. Moreover, E64d decreased the production of MDA and increased the activity of SOD. The results showed that E64d ameliorated ox-LDL-induced endothelial dysfunction in HAECs.

Transcriptome analysis of avian reovirus-mediated changes in gene expression of normal chicken fibroblast DF-1 cells

Background

Avian reovirus (ARV) is an important poultry pathogen that can cause immunosuppression. In this study, RNA-Seq technology was applied to investigate the transcriptome-wide changes of DF-1 cells upon ARV infection at the middle stage.

Results

Total RNA of ARV-infected or mock-infected samples at 10 and 18 h post infection (hpi) was extracted to build RNA-Seq datasets. Analysis of the sequencing data revealed that the expressions of numerous genes were altered, and a panel of differentially expressed genes were confirmed with RT-qPCR. At 10 hpi, 104 genes were down-regulated and 64 were up-regulated, while the expressions of 47 genes were increased and only one was down-regulated, which may play a role in retinoic acid biosynthesis, at 18 hpi in the ARV-infected cells. The similar profiles of up-regulated genes between the two groups of infected cells suggest that ARV infection activated a prolonged antiviral response of host cells. Alternative splicing analysis found no significantly changed events altered by ARV infection.

Conclusions

Overall, the differential expression profile presented in this study can be used to expand our understanding of the comprehensive interactions between ARV and the host cells, and may be helpful for us to reveal the pathogenic mechanism on the molecular level.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4310-5) contains supplementary material, which is available to authorized users.