Extracellular vesicles originating from autophagy mediate an antibody-resistant spread of classical swine fever virus in cell culture

Extracellular vesicles promote the infection and pathogenicity of Japanese encephalitis virus

Japanese encephalitis virus (JEV) is a neurotropic zoonotic pathogen that poses a serious threat to public health. Currently, there is no specific therapeutic agent available for JEV infection, primarily due to the complexity of its infection mechanism and pathogenesis. Extracellular vesicles (EVs) have been known to play an important role in viral infection, but their specific functions in JEV infection remain unknown. Here, ultracentrifugation in combination with density gradient centrifugation was conducted to purify EVs from JEV-infected cells. The purified EVs were found to be infectious, with virions observed inside the EVs. Furthermore, our study showed the formation process of virion-containing EVs both in vitro and in vivo, which involved the fusion of multivesicular bodies with the cell membrane, leading to the release of virion-containing intraluminal vesicles into the extracellular space. Further studies revealed that EVs played a crucial role in JEV propagation by facilitating viral entry and assembly-release. Furthermore, EVs assisted JEV in evading the neutralizing antibodies and promoted viral capability to cross the blood-brain and placental barriers. Moreover, in vivo experiments demonstrated that EVs were beneficial for JEV infection and pathogenicity. Taken together, our findings highlight the significant contribution of EVs in JEV infection and provide valuable insights into JEV pathogenesis.

CRISPR/Cas9-mediated knockout of STAT1 in porcine-derived cell lines to elucidate the role of STAT1 in autophagy following classical swine fever virus infection

Signal transducer and activator of transcription 1 (STAT1) plays a critical role in immune response, human STAT1 as a transcriptional suppressor of autophagy genes and autophagic activity. Classical swine fever virus (CSFV)-infected induce autophagy, leading to immune evasion. However, there are limited reports on the function of porcine STAT1 in autophagy during CSFV infection. There is also lack of suitable in vitro models for studying porcine STAT1. The objective of this study was to establish porcine PK-15 STAT1-/- and 3D4/21 STAT1-/- cell lines using the CRISPR/Cas9 system to investigate the function of the STAT1 in autophagy. The PK-15STAT1-/- and 3D4/21STAT1-/- cell lines, featuring homozygous knockout of STAT1 gene were successfully constructed using the CRISPR/Cas9 editing system. The knockout efficiency determined to be 82.4% and 81.1%, respectively. Infection with CSFV in porcine PK-15STAT1-/- and 3D4/21STAT1-/- cells led to an observable increase in autophagosomes as evidenced by transmission electron microscope. Additionally, STAT1 knockout (STAT1-/-) by the CRISPR/Cas9 system upregulated the expression of ULK1, Beclin1, and LC3 genes, thereby enhancing autophagy during CSFV infection. Conversely, overexpression of STAT1 downregulated the expression of ULK1, Beclin1, and LC3 genes, leading to inhibition of autophagy during CSFV infection.The application of an autophagy dual-fluorescent-tracking plasmid demonstrated that STAT1 knockout enhanced autophagy accumulation during CSFV infection, while STAT1 overexpression inhibited it. Moreover, the 3D4/21STAT1-/- cell line proved to be a more suitable in vitro model compared to the PK-15STAT1-/- cell line for elucidating the involvement of STAT1 in autophagy during CSFV infection.

The complexity of extracellular vesicles: Bridging the gap between cellular communication and neuropathology

Brain-derived extracellular vesicles (EVs) serve a prominent role in maintaining homeostasis and contributing to pathology in health and disease. This review establishes a crucial link between physiological processes leading to EV biogenesis and their impacts on disease. EVs are involved in the clearance and transport of proteins and nucleic acids, responding to changes in cellular processes associated with neurodegeneration, including autophagic disruption, organellar dysfunction, aging, and other cell stresses. In neurodegenerative disorders (e.g., Alzheimer's disease, Parkinson's disease, etc.), EVs contribute to the spread of pathological proteins like amyloid β, tau, ɑ-synuclein, prions, and TDP-43, exacerbating neurodegeneration and accelerating disease progression. Despite evidence for both neuropathological and neuroprotective effects of EVs, the mechanistic switch between their physiological and pathological functions remains elusive, warranting further research into their involvement in neurodegenerative disease. Moreover, owing to their innate ability to traverse the blood-brain barrier and their ubiquitous nature, EVs emerge as promising candidates for novel diagnostic and therapeutic strategies. The review uniquely positions itself at the intersection of EV cell biology, neurophysiology, and neuropathology, offering insights into the diverse biological roles of EVs in health and disease.

Exosomal circ_CCDC7/gga-miR-6568-3p/Pax7 axis accelerates the differentiation of chicken embryonic stem cells infected with subgroup J avian leukosis virus

Exosome-mediated horizontal and vertical transmission of subgroup J avian leukosis virus (ALV-J) in poultry flocks can lead to growth inhibition and severe immunosuppression. However, there are few reports on the early infection of chicken embryonic stem cells (cESCs) with ALV-J. In this study, we confirmed that early infection with ALV-J can accelerate the differentiation of cESCs and promote the secretion of exosomes. To investigate the modulation strategy of ALV-J in cESCs, circRNA sequencing was performed for further analysis. A total of 305 differentially expressed circRNAs (DECs) were obtained, including 71 upregulated DECs. Circ-CCDC7 was found to be the most upregulated DEC and was assessed by qRT-PCR, with the result consistent with the result of circRNA-seq. Based on qRT-PCR, gga-miR-6568-3p was found to be the target of the top 3 DECs, including circ-CCDC7, and the stem cell marker gene Pax7 was identified as the target gene of gga-miR-6568-3p. This study demonstrated that exosomal circ-CCDC7/gga-miR-6568-3p/Pax7 accelerates the differentiation of cESCs after early infection with ALV-J.

Exosomal miR-7-25207 Increases Subgroup J Avian Leukosis Virus Titers by Targeting the Akt-CyclinQ1 and PRC1-YAF2 Dual Pathways

Subgroup J avian leukosis virus (ALV-J) is a major pathogen in poultry, causing substantial economic losses to the poultry industry worldwide. Exosomal small RNAs derived from virus-infected cells or biological fluids can serve as viral transmission vectors. However, the role and mechanism of exosomal miRNA in ALV-J infection are unclear. In this study, we demonstrated that exosomal microRNA-7-25207 (miR-7-25207) could increase the titers of ALV-J. Exosomes isolated from ALV-J-infected DF-1 cells (Exo-ALV-J) contained partial viral proteins from ALV-J and could transmit the infection to uninfected DF-1 cells, leading to productive infection. Additionally, the RNA expression profile of exosomes was altered following ALV-J infection. miRNA analysis revealed that the expression of exosomal miR-7-25207 increased. Overexpression of miR-7-25207 significantly increased the titers of ALV-J in transfected cells. Furthermore, miR-7-25207 directly suppressed the expression of Akt and PRC1. Akt, in turn, directly inhibited CyclinQ1 expression, while PRC1 directly interfered with YAF2 expression. In conclusion, ALV-J infection activates the expression of miR-7-25207, which is subsequently delivered via exosomes to uninfected cells, increasing ALV-J titers by targeting Akt-CyclinQ1 and PRC1-YAF2 dual pathways. These findings suggest that exosomal miR-7-25207 may serve as a potential biomarker for clinical parameters in ALV-J infection.

EV71 5'UTR interacts with 3D protein affecting replication through the AKT-mTOR pathway

BACKGROUND

EV71 is one of the important pathogens of Hand-foot-and-mouth disease (HFMD), which causes serious neurological symptoms. Several studies have speculated that there will be interaction between 5'UTR and 3D protein. However, whether 5'UTR interacts with the 3D protein in regulating virus replication has not been clarified.

METHODS

Four 5'UTR mutation sites (nt88C/T, nt90-102-3C, nt157G/A and nt574T/A) and two 3D protein mutation sites (S37N and R142K) were mutated or co-mutated using virulent strains as templates. The replication of these mutant viruses and their effect on autophagy were determined.

RESULTS

5'UTR single-point mutant strains, except for EGFP-EV71(nt90-102-3C), triggered replication attenuation. The replication ability of them was weaker than that of the parent strain the virulent strain SDLY107 which is the fatal strain that can cause severe neurological complications. While the replication level of the co-mutant strains showed different characteristics. 5 co-mutant strains with interaction were screened: EGFP-EV71(S37N-nt88C/T), EGFP-EV71(S37N-nt574T/A), EGFP-EV71(R142K-nt574T/A), EGFP-EV71(R142K-nt88C/T), and EGFP-EV71(R142K-nt157G/A). The results showed that the high replicative strains significantly promoted the accumulation of autophagosomes in host cells and hindered the degradation of autolysosomes. The low replicative strains had a low ability to regulate the autophagy of host cells. In addition, the high replicative strains also significantly inhibited the phosphorylation of AKT and mTOR.

CONCLUSIONS

EV71 5'UTR interacted with the 3D protein during virus replication. The co-mutation of S37N and nt88C/T, S37N and nt574T/ A, R142K and nt574T/A induced incomplete autophagy of host cells and promoted virus replication by inhibiting the autophagy pathway AKT-mTOR. The co-mutation of R142K and nt88C/T, and R142K and nt157G/A significantly reduced the inhibitory effect of EV71 on the AKT-mTOR pathway and reduced the replication ability of the virus.

The protective effect of intranasal immunization with influenza virus recombinant adenovirus vaccine on mucosal and systemic immune response

Influenza virus is a kind of virus that poses several hazards of animal and human health. Therefore, it is important to develop an effective vaccine to prevent influenza. To this end we successfully packaged recombinant adenovirus rAd-NP-M2e-GFP expressing multiple copies of influenza virus conserved antigens NP and M2e and packaged empty vector adenovirus rAd-GFP. The effect of rAd-NP-M2e-GFP on the activation of dendritic cell (DC) in vitro and in vivo was detected by intranasal immunization. The results showed that rAd-NP-M2e-GFP promoted the activation of DC in vitro and in vivo. After the primary immunization and booster immunization of mice through the nasal immune way, the results showed that rAd-NP-M2e-GFP induced enhanced local mucosal-specific T cell responses, increased the content of SIgA in broncho alveolar lavage fluids (BALF) and triggered the differentiation of B cells in the germinal center. It is proved that rAd-NP-M2e-GFP can significantly elicit mucosal immunity and systemic immune response. In addition, rAd-NP-M2e-GFP could effectively protect mice after H1N1 influenza virus challenge. To lay the foundation and provide reference for further development of influenza virus mucosal vaccine in the future.

Characterization and functional analysis of SOCS9 from orange-spotted grouper (Epinephelus coioides) during virus infection

The suppressor of cytokine signaling (SOCS) proteins family have twelve members including eight known mammalian SOCS members (CISH, SOCS1-7) and four new discovery members (SOCS3b, SOCS5b, SOCS8 and SOCS9) that is regarded as a classic feedback inhibitor of cytokine signaling. Although the function of the mammalian SOCS proteins have been well studied, little is known about the roles of SOCS in fish during viral infection. In this study, the molecular characteristics of SOCS9 from orange-spotted grouper (Epinephelus coioides, EcSOCS9) is investigated. The EcSOCS9 protein encoded 543 amino acids with typical SH2 (389-475aa) and SOCS_box (491-527aa), sharing high identities with reported fish SOCS9. EcSOCS9 was expressed in all detected tissues and highly expressed in kidney. After red-spotted grouper nervous necrosis virus (RGNNV) infection, the expression of EcSOCS9 was significantly induced in vitro. Furthermore, EcSOCS9 overexpression enhanced RGNNV replication, promoted virus-induced mitophagy that evidenced by the increased level of LC3-Ⅱ, BCL2, PGAM5 and decreased level of BNIP3 and FUNDC1. Besides, EcSOCS9 overexpression suppressed the expression levels of ATP6, CYB, ND4, ATP level and induced ROS level. The expression levels of interferon (IFN) related factors (IRF1, IRF3, IRF7, P53), inflammatory factors (IL1-β, IL8, TLR2, TNF-α) and IFN-3, ISRE, NF-κB, AP1 activities were also reduced by overexpressing EcSOCS9. These date suggests that EcSOCS9 impacts RGNNV infection through modulating mitophagy, regulating the expression levels of IFN- related and inflammatory factors, which will expand our understanding of fish immune responses during viral infection.

Host Subcellular Organelles: Targets of Viral Manipulation

Viruses have evolved sophisticated mechanisms to manipulate host cell processes and utilize intracellular organelles to facilitate their replication. These complex interactions between viruses and cellular organelles allow them to hijack the cellular machinery and impair homeostasis. Moreover, viral infection alters the cell membrane's structure and composition and induces vesicle formation to facilitate intracellular trafficking of viral components. However, the research focus has predominantly been on the immune response elicited by viruses, often overlooking the significant alterations that viruses induce in cellular organelles. Gaining a deeper understanding of these virus-induced cellular changes is crucial for elucidating the full life cycle of viruses and developing potent antiviral therapies. Exploring virus-induced cellular changes could substantially improve our understanding of viral infection mechanisms.

The regulation of cell homeostasis and antiviral innate immunity by autophagy during classical swine fever virus infection

CSFV (classical swine fever virus) is currently endemic in developing countries in Asia and has recently re-emerged in Japan. Under the pressure of natural selection pressure, CSFV keeps evolving to maintain its ecological niche in nature. CSFV has evolved mechanisms that induce immune depression, but its pathogenic mechanism is still unclear. In this study, using transcriptomics and metabolomics methods, we found that CSFV infection alters innate host immunity by activating the interferon pathway, inhibiting host inflammation, apoptosis, and remodelling host metabolism in porcine alveolar macrophages. Moreover, we revealed that autophagy could alter innate immunity and metabolism induced by CSFV infection. Enhanced autophagy further inhibited CSFV-induced RIG-I-IRF3 signal transduction axis and JAK-STAT signalling pathway and blocked type I interferon production while reducing autophagy inhibition of the NF-κB signalling pathway and apoptosis in CSFV infection cells. Furthermore, the level of CSFV infection-induced glycolysis and the content of lactate and pyruvate, as well as 3-phosphoglyceraldehyde, a derivative of glycolysis converted to serine, was altered by autophagy. We also found that silencing HK2 (hexokinase 2), the rate-limiting enzyme of glycolytic metabolism, could induce autophagy but reduce the interferon signalling pathway, NF-κB signalling pathway, and inhibition of apoptosis induced by CSFV infection. In addition, inhibited cellular autophagy by silencing ATG5 or using 3-Methyladenine, could backfill the inhibitory effect of silencing HK2 on the cellular interferon signalling pathway, NF-κB signalling pathway, and apoptosis.

Trick-or-Trap: Extracellular Vesicles and Viral Transmission

Extracellular vesicles (EVs) are lipid membrane-enclosed particles produced by most cells, playing important roles in various biological processes. They have been shown to be involved in antiviral mechanisms such as transporting antiviral molecules, transmitting viral resistance, and participating in antigen presentation. While viral transmission was traditionally thought to occur through independent viral particles, the process of viral infection is complex, with multiple barriers and challenges that viruses must overcome for successful infection. As a result, viruses exploit the intercellular communication pathways of EVs to facilitate cluster transmission, increasing their chances of infecting target cells. Viral vesicle transmission offers two significant advantages. Firstly, it enables the collective transmission of viral genomes, increasing the chances of infection and promoting interactions between viruses in subsequent generations. Secondly, the use of vesicles as vehicles for viral transmission provides protection to viral particles against environmental factors, while also expanding the cell tropism allowing viruses to reach cells in a receptor-independent manner. Understanding the role of EVs in viral transmission is crucial for comprehending virus evolution and developing innovative antiviral strategies, therapeutic interventions, and vaccine approaches.

HDAC-Specific Inhibitors Induce the Release of Porcine Epidemic Diarrhea Virus via the COPII-Coated Vesicles

Porcine epidemic diarrhea virus (PEDV) is an alpha-coronavirus causing acute diarrhea and high mortality in neonatal suckling piglets, resulting in huge economic losses for the global swine industry. The replication, assembly and cell egression of PEDV, an enveloped RNA virus, are mediated via altered intracellular trafficking. The underlying mechanisms of PEDV secretion are poorly understood. In this study, we found that the histone deacetylase (HDAC)-specific inhibitors, trichostatin A (TSA) and sodium butyrate (NaB), facilitate the secretion of infectious PEDV particles without interfering with its assembly. We found that PEDV N protein and its replicative intermediate dsRNA colocalize with coat protein complex II (COPII)-coated vesicles. We also showed that the colocalization of PEDV and COPII is enhanced by the HDAC-specific inhibitors. In addition, ultrastructural analysis revealed that the HDAC-specific inhibitors promote COPII-coated vesicles carrying PEDV virions and the secretion of COPII-coated vesicles. Consistently, HDAC-specific inhibitors-induced PEDV particle secretion was abolished by Sec24B knockdown, implying that the HDAC-specific inhibitors-mediated COPII-coated vesicles are required for PEDV secretion. Taken together, our findings provide initial evidence suggesting that PEDV virions can assemble in the endoplasmic reticulum (ER) and bud off from the ER in the COPII-coated vesicles. HDAC-specific inhibitors promote PEDV release by hijacking the COPII-coated vesicles.

Exosomes mediate the antibody-resistant intercellular transmission of porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic enteric coronavirus that causes severe enteritis and lethal watery diarrhea in suckling piglets, leading to tremendous economic losses. Exosomes have been reported to participate in intercellular communication by the transportation of a variety of biological materials, including RNAs, lipids, and proteins. However, PEDV transmission routes have not yet been fully elucidated, and whether exosomes function in PEDV transmission remains unclear. In this study, we extracted and purified exosomes from PEDV-infected Vero cells using a stringent isolation method with a combination of chemical precipitation, ultracentrifugation, and incubation with CD63-labeled magnetic beads. We found that exosomes from PEDV-infected Vero cells contain viral genomic RNA and viral nucleocapsid protein. Furthermore, we demonstrated that the purified exosomes from PEDV-infected cells are capable of transmitting the virus to both PEDV-susceptible and non-susceptible cells. Importantly, exosome-mediated PEDV infection was resistant to neutralization by PEDV-specific neutralizing antibodies that potently neutralized free PEDV. Our study reveals a potential immune evasion mechanism utilized by PEDV and provides new insight into the transmission and infection of this important pathogen.