Paraoxonase-1 Facilitates PRRSV Replication by Interacting with Viral Nonstructural Protein-9 and Inhibiting Type I Interferon Pathway

Innate Immune Evasion of PRRSV nsp11 through Degradation of the HDAC2 by Its Endoribonuclease Activity

Porcine reproductive and respiratory syndrome virus (PRRSV), a member of the Arteriviridae family, represents a persistent menace to the global pig industry, causing reproductive failure and respiratory disease in pigs. In this study, we delved into the role of histone deacetylases (HDAC2) during PRRSV infection. Our findings revealed that HDAC2 expression is downregulated upon PRRSV infection. Notably, suppressing HDAC2 activity through specific small interfering RNA led to an increase in virus production, whereas overexpressing HDAC2 effectively inhibited PRRSV replication by boosting the expression of IFN-regulated antiviral molecules. Furthermore, we identified the virus's nonstructural protein 11 (nsp11) as a key player in reducing HDAC2 levels. Mutagenic analyses of PRRSV nsp11 revealed that its antagonistic effect on the antiviral activity of HDAC2 is dependent on its endonuclease activity. In summary, our research uncovered a novel immune evasion mechanism employed by PRRSV, providing crucial insights into the pathogenesis of this virus and guiding the development of innovative prevention strategies against PRRSV infection.

Highly pathogenic PRRSV upregulates IL-13 production through nonstructural protein 9-mediated inhibition of N6-methyladenosine demethylase FTO

Porcine reproductive and respiratory syndrome virus (PRRSV), a highly infectious virus, causes severe losses in the swine industry by regulating the inflammatory response, inducing tissue damage, suppressing the innate immune response, and promoting persistent infection in hosts. Interleukin-13 (IL-13) is a cytokine that plays a critical role in regulating immune responses and inflammation, particularly in immune-related disorders, certain types of cancer, and numerous bacterial and viral infections; however, the underlying mechanisms of IL-13 regulation during PRRSV infection are not well understood. In this study, we demonstrated that PRRSV infection elevates IL-13 levels in porcine alveolar macrophages. PRRSV enhances m6A-methylated RNA levels while reducing the expression of fat mass and obesity associated protein (FTO, an m6A demethylase), thereby augmenting IL-13 production. PRRSV nonstructural protein 9 (nsp9) was a key factor for this modulation. Furthermore, we found that the residues Asp567, Tyr586, Leu593, and Asp595 were essential for nsp9 to induce IL-13 production via attenuation of FTO expression. These insights delineate PRRSV nsp9's role in FTO-mediated IL-13 release, advancing our understanding of PRRSV's impact on host immune and inflammatory responses.

Classification, replication, and transcription of Nidovirales

Nidovirales is one order of RNA virus, with the largest single-stranded positive sense RNA genome enwrapped with membrane envelope. It comprises four families (Arterividae, Mesoniviridae, Roniviridae, and Coronaviridae) and has been circulating in humans and animals for almost one century, posing great threat to livestock and poultry，as well as to public health. Nidovirales shares similar life cycle: attachment to cell surface, entry, primary translation of replicases, viral RNA replication in cytoplasm, translation of viral proteins, virion assembly, budding, and release. The viral RNA synthesis is the critical step during infection, including genomic RNA (gRNA) replication and subgenomic mRNAs (sg mRNAs) transcription. gRNA replication requires the synthesis of a negative sense full-length RNA intermediate, while the sg mRNAs transcription involves the synthesis of a nested set of negative sense subgenomic intermediates by a discontinuous strategy. This RNA synthesis process is mediated by the viral replication/transcription complex (RTC), which consists of several enzymatic replicases derived from the polyprotein 1a and polyprotein 1ab and several cellular proteins. These replicases and host factors represent the optimal potential therapeutic targets. Hereby, we summarize the Nidovirales classification, associated diseases, "replication organelle," replication and transcription mechanisms, as well as related regulatory factors.

The crucial regulatory role of type I interferon in inflammatory diseases

Type I interferon (IFN-I) plays crucial roles in the regulation of inflammation and it is associated with various inflammatory diseases including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and periodontitis, impacting people's health and quality of life. It is well-established that IFN-Is affect immune responses and inflammatory factors by regulating some signaling. However, currently, there is no comprehensive overview of the crucial regulatory role of IFN-I in distinctive pathways as well as associated inflammatory diseases. This review aims to provide a narrative of the involvement of IFN-I in different signaling pathways, mainly mediating the related key factors with specific targets in the pathways and signaling cascades to influence the progression of inflammatory diseases. As such, we suggested that IFN-Is induce inflammatory regulation through the stimulation of certain factors in signaling pathways, which displays possible efficient treatment methods and provides a reference for the precise control of inflammatory diseases.

Antiviral Activity Against SARS-CoV-2 Variants Using in Silico and in Vitro Approaches

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emergence in 2019 led to global health crises and the persistent risk of viral mutations. To combat SARS-CoV-2 variants, researchers have explored new approaches to identifying potential targets for coronaviruses. This study aimed to identify SARS-CoV-2 inhibitors using drug repurposing. In silico studies and network pharmacology were conducted to validate targets and coronavirus-associated diseases to select potential candidates, and in vitro assays were performed to evaluate the antiviral effects of the candidate drugs to elucidate the mechanisms of the viruses at the molecular level and determine the effective antiviral drugs for them. Plaque and cytopathic effect reduction were evaluated, and real-time quantitative reverse transcription was used to evaluate the antiviral activity of the candidate drugs against SARS-CoV-2 variants in vitro. Finally, a comparison was made between the molecular docking binding affinities of fenofibrate and remdesivir (positive control) to conventional and identified targets validated from protein-protein interaction (PPI). Seven candidate drugs were obtained based on the biological targets of the coronavirus, and potential targets were identified by constructing complex disease targets and PPI networks. Among the candidates, fenofibrate exhibited the strongest inhibition effect 1 h after Vero E6 cell infection with SARS-CoV-2 variants. This study identified potential targets for coronavirus disease (COVID-19) and SARS-CoV-2 and suggested fenofibrate as a potential therapy for COVID-19.