Proteome Analysis in PAM Cells Reveals That African Swine Fever Virus Can Regulate the Level of Intracellular Polyamines to Facilitate Its Own Replication through ARG1

Identification and verification of the role of key metabolites and metabolic pathways on ASFV replication

African swine fever virus (ASFV) infection usually causes viremia within a few days. However, the metabolic changes in pig serum after ASFV infection remain unclear. In this study, serum samples collected from ASFV-infected pigs at different times were analyzed using pseudotargeted metabolomics method. Metabolomic analysis revealed the dopaminergic synapse pathway has the highest rich factor in both ASFV5 and ASFV10 groups. By disrupting the dopamine synaptic pathway, dopamine receptor antagonists inhibited ASFV replication and L-dopa promoted ASFV replication. In addition, guanosine, one of the top20 changed metabolites in both ASFV5 and ASFV10 groups suppressed the replication of ASFV. Taken together, this study revealed the changed serum metabolite profiles of ASFV-infected pigs at various times after infection and verified the effect of the changed metabolites and metabolic pathways on ASFV replication. These findings may contribute to understanding the pathogenic mechanisms of ASFV and the development of target drugs to control ASF.

TRAF3 gene regulates macrophage migration and activation by lung epithelial cells infected with Aspergillus fumigatus

IMPORTANCE

Aspergillus fumigatus can infect immunocompromised individuals and cause chronic and fatal invasive fungal infections. A better understanding of the molecular mechanisms of A. fumigatus-host interactions may provide new references for disease treatment. In this study, we demonstrated that the TRAF3 gene plays an important role in the early infection of A. fumigatus by regulating the resistance of lung epithelial cells to A. fumigatus. Macrophages are the most abundant innate immune cells in the alveoli; however, few studies have reported on the interactions between lung epithelial cells and macrophages in response to A. fumigatus invasion. In our study, it was demonstrated that the TRAF3 gene reduces migration to macrophages and cytokine production by negatively regulating lung epithelial cell adhesion and internalization of A. fumigatus spores. Together, our results provide new insights into lung epithelial cell-macrophage interactions during A. fumigatus infection.

Quantitative proteomics based on TMT revealed the response of PK15 cells infected PEDV wild strain

Porcine epidemic diarrhea (PED), caused by porcine epidemic diarrhea virus (PEDV), is an acute and highly contagious enteric disease with a high mortality rate in suckling piglets. Identification of proteins associated with PEDV infection may provide insights into the pathogenesis of this viral disease. In this study, we employed tandem mass tag (TMT) quantitative protein analysis to investigate proteomic changes in PK15 cells following PEDV infection, and differential protein expression profiles were obtained at 0 h, 24 h, and 48 h post-infection. Overall, a total of 6330 proteins were identified. Applying criteria for fold change >1.5 < 0.67 and p-values <0.05 resulted in the identification of 59 up-regulated proteins and 103 down-regulated proteins that exhibited significant alterations in the H24 group compared to the H0 group. The H48 group demonstrated significant upregulation of 110 proteins and downregulation of 144 proteins compared to the H0 group; additionally, there were also 10 upregulated and 30 downregulated proteins in the H48 group when compared to the H24 group. These differentially expressed proteins (DEPs) were involved in immune response regulation, signal transduction, lipid transport and metabolism processes as well as cell apoptosis pathways. Based on these DEPs, we propose that PEDV may disrupt signal transduction pathways along with lipid transport and metabolism processes leading to maximal viral replication, it may also trigger inflammatory cascades accordingly. These findings could provide valuable information for elucidating specific pathogenesis related to PEDV infection while contributing towards developing new antiviral strategies.

Metabolomic analysis of pig spleen reveals African swine fever virus infection increased acylcarnitine levels to facilitate viral replication

African swine fever (ASF) is a devastating disease caused by the African swine fever virus (ASFV) that adversely affects the pig industry. The spleen is the main target organ of ASFV; however, the function of metabolites in the spleen during ASFV infection is yet to be investigated. To define the metabolic changes in the spleen after ASFV infection, untargeted and targeted metabolomics analyses of spleens from ASFV-infected pigs were conducted. Untargeted metabolomics analysis revealed 540 metabolites with significant differential levels. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that these metabolites were mainly enriched in metabolic pathways, including nucleotide metabolism, purine metabolism, arginine biosynthesis, and neuroactive ligand-receptor interaction. Moreover, 134 of 540 metabolites quantified by targeted metabolomics analysis had differential levels and were enriched in metabolic pathways such as the biosynthesis of cofactors, ABC transporters, and biosynthesis of amino acids. Furthermore, coalition analysis of untargeted and targeted metabolomics data revealed that the levels of acylcarnitines, which are intermediates of fatty acid β-oxidation, were significantly increased in ASFV-infected spleens compared with those in the uninfected spleens. Moreover, inhibiting fatty acid β-oxidation significantly reduced ASFV replication, indicating that fatty acid β-oxidation is essential for this process. To our knowledge, this is the first report presenting the metabolite profiles of ASFV-infected pigs. This study revealed a new mechanism of ASFV-mediated regulation of host metabolism. These findings provide new insights into the pathogenic mechanisms of ASFV, which will benefit the development of target drugs for ASFV replication. IMPORTANCE African swine fever virus, the only member of the Asfarviridae family, relies on hijacking host metabolism to meet the demand for self-replication. However, the change in host metabolism after African swine fever virus (ASFV) infection remains unknown. Here, we analyzed the metabolic changes in the pig spleen after ASFV infection for the first time. ASFV infection increased the levels of acylcarnitines. Inhibition of the production and metabolism of acylcarnitines inhibited ASFV replication. Acylcarnitines are the vital intermediates of fatty acid β-oxidation. This study highlights the critical role of fatty acid β-oxidation in ASFV infection, which may help identify target drugs to control African swine fever disease.

PI3K-Akt pathway-independent PIK3AP1 identified as a replication inhibitor of the African swine fever virus based on iTRAQ proteomic analysis

African swine fever (ASF) is a severe infectious disease that has a high global prevalence. The fatality rate of pigs infected with ASF virus (ASFV) is close to 100%; in the absence of a safe and reliable commercial vaccine, this poses a threat to the global pig industry and public health. To better understand the interaction of ASFV with its host, isobaric tags for relative and absolute quantitation combined with liquid chromatography-mass spectrometry was used to conduct quantitative proteomic analysis of bone marrow-derived macrophage cells infected with ASFV. Overall, 4579 proteins were identified; 286 of these were significantly upregulated and 69 were significantly downregulated after ASFV infection. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and protein-protein interaction network analyses were used to obtain insights into the dynamics and complexity of the ASFV-host interaction. In addition, immunoblotting revealed that the expression of PIK3AP1, RNF114, and FABP5 was upregulated and that of TRAM1 was downregulated after ASFV infection. Overexpression of PIK3AP1 and RNF114 significantly inhibited ASFV replication in vitro, but the suppressive effect of PIK3AP1 on ASFV replication was independent of the PI3K-Akt pathway. Further studies confirmed that ASFV MGF360-9L interacts with PIK3AP1 to reduce its protein expression level. Moreover, LY294002, an inhibitor of the PI3K-Akt pathway, inhibited ASFV replication, indicating the importance of the PI3K-Akt pathway in ASFV infection. This study identified the network of interactions between ASFV and host cells and provides a reference for the development of anti-ASFV strategies and for studying the potential mechanisms and pathogenesis of ASFV infection.

Infection Characteristics and Transcriptomics of African Swine Fever Virus in Bama Minipigs

Animal experiments on African swine fever virus (ASFV) are vital to the study of ASFV; however, ASFV can only infect pigs, and animal experiments need to be performed in animal biosafety level 3 (ABSL-3) laboratories, meaning that many small ABSL-3 laboratories are unable to carry out in vivo ASFV experiments. Therefore, miniaturized experimental animals for ASFV infection are urgently needed. Here, we successfully isolated genotype II of ASFV SY-1 from wild boars and evaluated ASFV-infected Bama minipigs in a negative-pressure isolator of a small ABSL-3 laboratory. The pathological changes of ASFV-infected Bama minipigs were consistent with characteristic lesions of ASFV-infected domestic pigs and wild boars. All pigs died 5 to 14 days postinfection (dpi) through intramuscular injection. Viral genomic DNA from nasal, oral, and rectal swab samples was first detectable at 2 to 4 dpi. The common differentially expressed genes were clustered in the immune-related, metabolic, and inflammatory response pathways from the spleen and inguinal lymph node samples comparing infected to mock. In summary, these results demonstrated that the Bama minipig was an appropriate model for ASFV infection in small ABSL-3 laboratories that can accelerate the research of vaccines and antiviral drugs and uncover pathogenic mechanisms of ASFV infection. IMPORTANCE African swine fever virus (ASFV) can only infect pigs rather than other animals. However, the domestic pigs cannot be kept in small ABSL-3 laboratories for a long time due to the characteristics of rapid growth and large size, which hinder ASFV research, including research of vaccines, antiviral drugs, and mechanisms. In contrast, Bama minipigs have unique advantages consisting of low growth and small size. In the research, Bama minipigs were used to evaluate the characteristics of ASFV infection in small ABSL-3 laboratories. The pathological changes, viral shedding, and gene regulation were consistent with those of domestic pigs infected with ASFV. Therefore, Bama minipigs can be a suitable model for ASFV infection in small ABSL-3 laboratories.

African swine fever virus infection activates inflammatory responses through downregulation of the anti-inflammatory molecule C1QTNF3

African swine fever (ASF) is the most dangerous pig disease, and causes enormous economic losses in the global pig industry. However, the mechanisms of ASF virus (ASFV) infection remains largely unclear. Hence, this study investigated the host response mechanisms to ASFV infection. We analyzed the differentially expressed proteins (DEPs) between serum samples from ASFV-infected and uninfected pigs using quantitative proteomics. Setting the p-value &lt; 0.05 and |log2 (fold change)| &gt; 1.5, we identified 173 DEPs, comprising 57 upregulated and 116 downregulated proteins, which belonged to various biological processes and pathways based on the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. The enriched pathways include immune responses, metabolism, and inflammation signaling pathways. Western blot analysis validated the DEPs identified using quantitative proteomics. Furthermore, our proteomics data showed that C1QTNF3 regulated the inflammatory signaling pathway. C1QTNF3 knockdown led to the upregulation of pro-inflammatory factors IL-1β, IL-8, and IL-6, thus inhibiting ASFV replication. These results indicated that C1QTNF3 was critical for ASFV infection. In conclusion, this study revealed the molecular mechanisms underlying the host-ASFV interaction, which may contribute to the development of novel antiviral strategies against ASFV infection in the future.

Proteome Analysis of Swine Macrophages after Infection with Two Genotype II African Swine Fever Isolates of Different Pathogenicity

Since the introduction of a highly pathogenic genotype II isolate of the African swine fever virus (ASFV) into Georgia in 2007, African swine fever (ASF) has gone panzootic. Outbreaks have been reported in Europe, Asia and, more recently, Latin America. Thus, ASFV has become a major threat to the pig industry worldwide, as broadly applicable vaccines are not available. While the majority of ASFV strains show high virulence in domestic pigs and wild boar, variations within the ASFV genome have resulted in the emergence of attenuated strains with low or moderate virulence. However, the molecular basis of the differences in virulence has not yet been discovered. To reveal virulence-associated protein expression patterns, we analysed the proteomes of the natural target cells of ASFV, primary porcine macrophages, after infection with two genotype II ASFV strains displaying high (Armenia 2008) and moderate (Estonia 2014) virulence using quantitative mass spectrometry. Very similar expression patterns were observed for the viral genes, and any differences were limited to the deletions within the Estonia 2014 genome. In addition to the canonical ASFV proteins, twelve novel protein products from recently described transcripts were confirmed in both isolates. Pathway analyses showed that both isolates evoked a similar host proteome response, despite their difference in virulence. However, subtle differences in the manipulation of the proteins involved in the proinflammatory response mediated by the MAPK14/p38 signalling cascade were observed.

A simple nanobody-based competitive ELISA to detect antibodies against African swine fever virus

African swine fever virus (ASFV) infection is a big threat to the global pig industry. Because there is no effective vaccine, rapid, low-cost, and simple diagnosis methods are necessary to detect the ASFV infection in pig herds. Nanobodies, with advantages of small molecular weight and easy genetic engineering, have been universally used as reagents for developing diagnostic kits. In this study, the recombinant ASFV-p30 was expressed and served as an antigen to immunize the Bactrian camel. Then, seven nanobodies against ASFV-p30 were screened using phage display technique. Subsequently, the seven nanobodies fused horseradish peroxidase (nanobody-HRP) were secretory expressed and one fusion protein ASFV-p30-Nb75-HRP was selected with the highest sensitivity in blocking ELISA. Using the ASFV-p30-Nb75-HRP fusion protein as a probe, a competitive ELISA (cELISA) was developed for detecting anti-ASFV antibodies in pig sera. The cut-off value of cELISA was determined to be 22.7% by testing 360 negative pig sera. The detection limit of the cELISA for positive pig sera was 1:320, and there was no cross-reaction with anti-other swine virus antibodies. The comparative assay showed that the agreement of the cELISA with a commercial ELISA kit was 100%. More importantly, the developed cELISA showed low cost and easy production as a commercial kit candidate. Collectively, a simple nanobody-based cELISA for detecting antibodies against ASFV is developed and it provides a new method for monitoring ASFV infection in the pig herds.

Proteomic Investigation Reveals Eukaryotic Translation Initiation Factor 5A Involvement in Porcine Reproductive and Respiratory Syndrome Virus Infection in vitro

Porcine reproductive and respiratory syndrome virus (PRRSV), one of the most serious animal pathogens in the world, has caused enormous global swine industry losses. An in-depth investigation of the PRRSV-host interaction would be beneficial for preventing and controlling PRRSV infections and transmission. In this study, we performed label-free quantitative proteomic assays to investigate proteome dynamics of porcine alveolar macrophages (PAMs) during infection with highly pathogenic PRRSV (HP-PRRSV) strain HN07-1. Analysis of the results led to identification of 269 significantly differentially expressed host cellular proteins, of which levels of proteins belonging to the eukaryotic translation initiation factor (eIF) family were found to be decreased in abundance in HP-PRRSV-infected PAMs. Furthermore, knockdown of eIF5A expression was demonstrated to markedly suppress HP-PRRSV propagation, as reflected by reduced progeny virus titers in vitro. These results highlight the importance of eIF5A in PRRSV infection, while also demonstrating that PAMs down-regulate eIF5A expression as a host cell antiviral strategy. Results of the current study deepen our understanding of PRRSV pathogenesis and provide novel insights to guide development of effective strategies to combat the virus.

Adaptive Cellular Immunity against African Swine Fever Virus Infections

African swine fever virus (ASFV) remains a threat to global pig populations. Infections with ASFV lead to a hemorrhagic disease with up to 100% lethality in Eurasian domestic and wild pigs. Although myeloid cells are the main target cells for ASFV, T cell responses are impacted by the infection as well. The complex responses remain not well understood, and, consequently, there is no commercially available vaccine. Here, we review the current knowledge about the induction of antiviral T cell responses by cells of the myeloid lineage, as well as T cell responses in infected animals, recent efforts in vaccine research, and T cell epitopes present in ASFV.

PEDV infection affects the expression of polyamine-related genes inhibiting viral proliferation

Porcine epidemic diarrhea virus (PEDV) is an alpha-coronavirus that causes epidemic diarrhea in swines. The mortality of PEDV infection in one-week-old piglets is extremely high, which causes a huge significant economic loss to the global pig husbandry and blocks its healthy development. There was a lack of adequate studies to elucidate pathogenic mechanism associated with PEDV infection. In the present study, we detected the expression profiles of polyamine metabolism associated genes in Vero cells infected with PEDV by RT-qPCR. It is shown that PAOX(acetylpolyamine oxidase), SMOX(spermine oxidase), SAT1(spermidine-spermine acetyltransferase 1), ODC1(ornithine decarboxylase 1), DHPS(deoxyhypusine synthase) and EIF5A( eukaryotic initiation factor 5A) were significantly upregulated. Through intervening SAT1 level in PEDV-infected Vero cells, it is identified that overexpression of SAT1 inhibited PEDV replication by reducing polyamine levels. Furthermore, polyamine depletion and upregulation were found to regulate the proliferation of PEDV. PEDV infection in Vero cells did not result in a significant change in the protein level of eIF5A, and in addition, the activated eIF5A did not affect the proliferation of PEDV. Our results provided new insights into the influence of polyamine metabolism on the proliferation of PEDV.

Development of a Dual ELISA for the Detection of CD2v-Unexpressed Lower-Virulence Mutational ASFV

African swine fever virus (ASFV) is an important viral pathogen infecting pigs worldwide throughout the pig industry. CD2v (an outer-membrane glycosylated protein of ASFV)-unexpressed lower-virulence mutants have appeared in China and other countries in recent years. Using OIE-recommended quantitative PCR and ELISA methods, people can accurately judge whether pigs are infected with wild-type ASFV. However, the strategy has failed to distinguish ΔCD2v lower-virulence mutants and wild-type ASFV infection. Here, we expressed and purified the CD2v and p30 proteins via CHO cells and successfully established a dual enzyme-linked immunosorbent assay (ELISA), which can be used to differentiate pigs infected with wild-type ASFV or with CD2v-unexpressed lower-virulence mutants. The dual ELISA showed excellent specificity without cross-reactions with antibodies of PRRSV, CSFV, JEV, PRV, or PPV. The dual ELISA could detect ASFV-infected positive serum samples up to dilutions of 5120 times, possessing high sensitivity. Therefore, the application of this dual ELISA approach can play an important role in ASFV epidemiology study and fill the gaps in differential diagnosis.

Comparison of the Proteomes of Porcine Macrophages and a Stable Porcine Cell Line after Infection with African Swine Fever Virus

African swine fever virus (ASFV), causing an OIE-notifiable viral disease of swine, is spreading over the Eurasian continent and threatening the global pig industry. Here, we conducted the first proteome analysis of ASFV-infected primary porcine monocyte-derived macrophages (moMΦ). In parallel to moMΦ isolated from different pigs, the stable porcine cell line WSL-R was infected with a recombinant of ASFV genotype IX strain “Kenya1033”. The outcome of the infections was compared via quantitative mass spectrometry (MS)-based proteome analysis. Major differences with respect to the expression of viral proteins or the host cell response were not observed. However, cell-specific expression of some individual viral proteins did occur. The observed modulations of the host proteome were mainly related to cell characteristics and function. Overall, we conclude that both infection models are suitable for use in the study of ASFV infection in vitro.