Effective inhibition of porcine transmissible gastroenteritis virus replication in ST cells by shRNAs targeting RNA-dependent RNA polymerase gene

All-Trans Retinoic Acid Attenuates Transmissible Gastroenteritis Virus-Induced Apoptosis in IPEC-J2 Cells via Inhibiting ROS-Mediated P38MAPK Signaling Pathway

Transmissible gastroenteritis virus (TGEV) can cause diarrhea, dehydration, and high mortality in piglets, which is closely related to intestinal epithelial cell apoptosis caused by TGEV infection. All-trans retinoic acid (ATRA) is the active metabolite of vitamin A, which has antioxidant and anti-apoptotic properties. However, it is unknown whether ATRA can attenuate TGEV-induced IPEC-J2 cells apoptosis. Therefore, we investigated the protective effects of ATRA on TGEV-induced apoptosis of IPEC-J2 cells and explored the potential molecular mechanism. Our results indicated that TGEV infection caused IPEC-J2 cells damage and apoptosis. However, ATRA treatment attenuated TGEV-induced IPEC-J2 cells damage by upregulating the mRNA expressions of ZO-1, Occludin, and Mucin-1. ATRA treatment also attenuated TGEV-induced apoptosis in IPEC-J2 cells by downregulating the expression of Caspase-3, which is related to the inhibition of death receptor (Fas and Caspase-8) and mitochondrial (Bax, Bcl-2, and Caspase-9) pathways. Moreover, ATRA treatment prevented TGEV-induced ROS and MDA production and the upregulation of P₃₈MAPK phosphorylation level, which is related to the increase in the activities of antioxidant enzymes (SOD, CAT, and T-AOC) and the mRNA abundance of antioxidant-related genes (GPX1, GPX2, SOD1, CAT, GCLC, and GCLM). In addition, treatment of TGEV-infected IPEC-J2 cells with the ROS inhibitors (NAC) significantly reduced the protein levels of p-P₃₈MAPK, Fas, Bax, and Cleaved-caspase-3 and the percentage of apoptotic cells. Our results indicated that ATRA attenuated TGEV-induced apoptosis in IPEC-J2 cells via improving the antioxidant capacity, thereby inhibiting the cell damage. the mechanism of which is associated with the inhibition of ROS-mediated P₃₈MAPK signaling pathway.

All-Trans Retinoic Acid Attenuates Transmissible Gastroenteritis Virus-Induced Inflammation in IPEC-J2 Cells via Suppressing the RLRs/NF-κB Signaling Pathway

Transmissible gastroenteritis virus (TGEV) infection can cause transmissible gastroenteritis (TGE), especially in suckling piglets, resulting in a significant economic loss for the global pig industry. The pathogenesis of TGEV infection is closely related to intestinal inflammation. All-trans retinoic acid (ATRA) has anti-inflammatory activity and immunomodulatory properties, but it is unclear whether ATRA can attenuate the inflammatory response induced by TGEV. This study aimed to investigate the protective effect of ATRA on TGEV-induced inflammatory injury in intestinal porcine epithelial cells (IPEC-J2) and to explore the underlying molecular mechanism. The results showed that TGEV infection triggered inflammatory response and damaged epithelial barrier integrity in IPEC-J2 cells. However, ATRA attenuated TGEV-induced inflammatory response by inhibiting the release of pro-inflammatory cytokines, including IL-1β, IL-6, IL-8 and TNF-α. ATRA also significantly reversed the reduction of ZO-1 and Occludin protein levels induced by TGEV infection and maintained epithelial barrier integrity. Moreover, ATRA treatment significantly prevented the upregulation of IкBα and NF-κB p65 phosphorylation levels and the nuclear translocation of NF-кB p65 induced by TGEV. On the other hand, treatment of TGEV-infected IPEC-J2 cells with the NF-κB inhibitors (BAY11-7082) significantly decreased the levels of inflammatory cytokines. Furthermore, ATRA treatment significantly downregulated the mRNA abundance and protein levels of TLR3, TLR7, RIG-I and MDA5, and downregulated their downstream signaling molecules TRIF, TRAF6 and MAVS mRNA expressions in TGEV-infected IPEC-J2 cells. However, the knockdown of RIG-I and MDA5 but not TLR3 and TLR7 significantly reduced the NF-κB p65 phosphorylation level and inflammatory cytokines levels in TGEV-infected IPEC-J2 cells. Our results indicated that ATRA attenuated TGEV-induced IPEC-J2 cells damage via suppressing inflammatory response, the mechanism of which is associated with the inhibition of TGEV-mediated activation of the RLRs/NF-κB signaling pathway.

A high-throughput drug screening strategy against coronaviruses

The emergence and re-emergence of coronaviruses (CoV) continually cause circulating epidemics and pandemics worldwide, such as the on-going outbreak of the novel coronavirus SARS-CoV-2. The resultant disease, coronavirus disease 2019 (COVID-19), has rapidly developed into a worldwide pandemic, leading to severe health and economic burdens. Although the recently announced vaccines against COVID-19 has rekindled hope, there is still a major challenge to urgently meet the global need for rapid treatment of the pandemic. Given the urgency of the CoV outbreak, we propose a strategy to screen potential broad-spectrum drugs against CoV in a high-throughput manner, particularly against SARS-CoV-2. Since the essential functional domains of CoV are extensively homologous, the availability of two types of mild CoV, HCoV-OC43 and MHV, should provide a valuable tool for the rapid identification of promising drugs against CoV without the drawbacks of level three biological confinements. The luciferase reporter gene is introduced into HCoV-OC43 and MHV to indicate viral activity, and hence the antiviral efficiency of screened drugs can be quantified by luciferase activity. Compounds with antiviral activity against both HCoV-OC43 and MHV are further evaluated in SARS-CoV-2 after structural optimizations. This system allows large-scale compounds to be screened to search for broad-spectrum drugs against CoV in a high-throughput manner, providing potential alternatives for clinical management of SARS-CoV-2 or other CoV.

Inhibition of porcine transmissible gastroenteritis virus infection in porcine kidney cells using short hairpin RNAs targeting the membrane gene

The membrane (M) protein is the most abundant component of the porcine transmissible gastroenteritis virus (TGEV) particle. To exploit the possibility of using RNA interference (RNAi) as a strategy against TGEV infection, three plasmids (pRNAT-1, pRNAT-2, and pRNAT-3) expressing short hairpin RNAs were designed to target three different coding regions of the M gene of TGEV. The plasmids were constructed and transiently transfected into a porcine kidney cells, PK-15, to determine whether these constructs inhibited TGEV production. The analysis of cytopathic effects demonstrated that pRNAT-2 and pRNAT-3 could protect PK-15 cells against pathological changes specifically and efficiently. Additionally, indirect immunofluorescence and 50% tissue culture infectious dose (TCID₅₀) assays showed that pRNAT-2 and pRNAT-3 inhibited the multiplication of the virus at the protein level effectively. Quantitative real-time PCR further confirmed that the amounts of viral RNAs in cell cultures pre-transfected with the three plasmids were reduced by 13, 68, and 70%, respectively. This is the first report showing that RNAi targeting of the M gene. Our results could promote studies of the specific function of viral genes associated with TGEV infection and might provide a theoretical basis for potential therapeutic applications.

RNA interference targeting nucleocapsid protein inhibits porcine reproductive and respiratory syndrome virus replication in Marc-145 cells

Porcine reproductive and respiratory syndrome (PRRS) is an important disease, which leads to severe economic losses in swine-producing areas of the world. However, current antiviral strategies cannot provide highly effective protection. In this study, three theoretically effective interference target sites (71–91, 144–164, 218–238) targeting the nucleocapsid (N) gene of PRRSV were designed and selected, and then three siRNA-expressing plasmids were constructed, respectively named p2.1-N71, p2.1-N144, and p2.1-N218. The recombinant siRNA-expressing plasmids were transfected into Marc-145 cells; then the cells were infected with PRRSV (JL07SW strain); finally, after incubation for 48 h, the antiviral activity of those siRNA-expressing plasmids in Marc-145 cells was assessed by cytopathic effects, virus titers, indirect immunofluorescence, and quantitative real-time PCR. Experimental results demonstrated that these three siRNA-expressing plasmids could effectively and significantly inhibit the replication of PRRSV by 93.2%, 83.6%, and 89.2% in Marc-145 cells, respectively. Among these three siRNA-expressing plasmids, p2.1-N71 was found to be most effective, while p2.1-N144 and p2.1-N218 displayed relatively weak inhibition of virus replication. The results indicated that siRNA-expressing plasmids targeting the N gene of PRRSV could significantly inhibit PRRSV replication in Marc-145 cells. Based on our experimental results and previous reports, the 71–91, 179–197, and 234–252 sites of the N gene are good choices to effectively inhibit the replication of PRRSV, and this RNA interference technique can be a potential anti-PRRSV strategy.

In vitro inhibition of transmissible gastroenteritis coronavirus replication in swine testicular cells by short hairpin RNAs targeting the ORF 7 gene

Background

Transmissible gastroenteritis (TGE) is a highly contagious viral disease of swine, characterized by severe vomiting, diarrhea, and high mortality. Currently, the vaccines for it are only partially effective and no specific drug is available for treatment of TGE virus (TGEV) infection. RNA interference has been confirmed as a new approach for controlling viral infections. In this study, the inhibitory effect of short hairpin RNAs (shRNAs) targeting the ORF 7 gene of TGEV on virus replication was examined.

Results

Four theoretically effective sequences of TGEV ORF 7 gene were designed and selected for construction of shRNA expression plasmids. In the reporter assays, three of four shRNA expression plasmids were able to inhibit significantly the expression of ORF 7 gene and replication of TGEV, as shown by real-time quantitative RT-PCR analysis of viral ORF 7 and N genes and detection of virus titers (TCID₅₀/ml). Stable swine testicular (ST) cells expressing the shRNAs were established. Observation of the cytopathic effect and apoptosis, as well as a cell proliferation assay demonstrated that the three shRNAs were capable of protecting ST cells against TGEV destruction, with high specificity and efficiency.

Conclusions

Our results indicated that plasmid-transcribed shRNAs targeting the ORF 7 gene in the TGEV genome effectively inhibited expression of the viral target gene and viral replication in vitro. These findings provide evidence that the shRNAs have potential therapeutic application for treatment of TGE.

Inhibition of porcine hemagglutinating encephalomyelitis virus replication by short hairpin RNAs targeting of the nucleocapsid gene in a porcine kidney cell line

Porcine hemagglutinating encephalomyelitis virus (PHEV), which causes porcine encephalomyelitis and is widespread among swine worldwide. RNA interference (RNAi) pathways have emerged as important regulators of virus–host cell interactions. In this study, two siRNA expression plasmids (shN1 and shN2) were generated to target two different coding regions of the nucleocapsid protein (N) of PHEV. The shRNAs were transiently transfected into a porcine kidney cell line, PK-15, to determine whether these constructs inhibited PHEV production. Our results revealed that both shRNAs were highly capable of inhibiting viral RNA genome replication, especially shN2. Next, stable transfection of shN2 was used to produce two siRNA stably expressing PK-15 cell clones (shN2-1 and shN2-2), and these two lines were infected with PHEV. The analysis of cytopathic effects (CPE) demonstrated that shN2-1 and shN2-2 were capable of protecting cells against PHEV infection with high specificity and efficiency. Furthermore, effective inhibition of viral replication persisted for up to 120 h by a TCID₅₀ assay. These results indicated that RNAi targeting of the N gene could facilitate studies of the specific function of viral genes associated with PHEV replication and may have potential therapeutic applications.

In vitro inhibition of porcine hemagglutinating encephalomyelitis virus replication with siRNAs targeting the spike glycoprotein and replicase polyprotein genes

Objective

The specific effect of RNA interference on the replication of porcine hemagglutinating encephalomyelitis virus (PHE-CoV) was explored.

Methods

Four species of small interfering RNA (siRNA), targeting different regions of the PHE-CoV spike glycoprotein and replicase polyprotein genes, were prepared by in vitro transcription. After transfection of PK-15 cells with each of the siRNAs followed by infection with PHE-CoV, the cytopathic effect (CPE) was examined by phase-contrast microscope, and viral proliferation within cells was examined by indirect immunofluorescence microscopy, hemagglutination (HA) test, TCID₅₀ assay and real-time RT-PCR.

Results

Examination of CPE demonstrated that the four siRNAs were capable of protecting cells against PHE-CoV invasion with very high specificity and efficiency. At 48 h post-infection, only a few siRNA-treated cells were positive for viral antigen staining, whereas most untreated virus-infected cells were positive. Transfection with siRNAs also suppressed the production of infectious virus by up to 18- to 32-fold as assessed by a HA test and 93- to 494-fold as assessed by TCID₅₀ assay. Furthermore, treatment with siRNAs caused a 53-91% reduction in the viral genome copy number as assessed by real-time RT-PCR.

Conclusion

These results suggested that the four species of siRNAs can efficiently inhibit PHE-CoV genome replication and infectious virus production.

Inhibition of porcine transmissible gastroenteritis virus (TGEV) replication in mini-pigs by shRNA

Transmissible gastroenteritis virus (TGEV) is the causative agent of porcine transmissible gastroenteritis (TGE), characterized by high mortality and severely retarded growth in piglets that dramatically affects the porcine industry. Previously, we have identified two shRNA-expressing plasmids pEGFP-U6/P1 and pEGFP-U6/P2 that target RNA-dependent RNA polymerase (RdRP) gene of TGEV with more than 95% of virus inhibition in vitro. In this study, inhibition of the TGEV replication by pEGFP-U6/P1 and pEGFP-U6/P2 was tested in mini-pigs. SPF mini-pigs at 25 days old were injected with the shRNA-expressing plasmids and then infected with TGEV. The results from the analyses of clinical signs, histopathology, indirect immunofluorescence (IIF) and RT-PCR show that the two shRNA-expressing plasmids could significantly decrease the quantity of TGEV in different organs and protect mini-pigs from TGEV infection. These findings illustrate the prospect for TGEV-specific shRNAs to be new anti-TGEV agents.

RNA interference targeting nucleocapsid protein (C) inhibits classical swine fever virus replication in SK-6 cells

The application of RNA interference (RNAi) strategy for controlling classical swine fever could become a promising alternative to the conventional eradication measures, as it was recently shown for foot-and-mouth disease (Chen et al., 2004), influenza (Ge et al., 2003), porcine reproductive and respiratory syndrome (He et al., 2007) and porcine transmissible gastroenteritis (Zhou et al., 2007). The use of synthetic siRNA which is corresponding to nucleotides 1130-1148 of the CSF virus strain Alfort, targeting the nucleocapsid protein (C) was investigated to show the inhibition of CSF virus replication. It could be shown that the virus titer of infected cells, which had been mock-transfected or transfected with control (non-silence) RNA were not affected. These data indicate that siRNA_253 is able to inhibit viral replication.

Identification and characterisation of the porcine 7SK RNA polymerase III promoter for short hairpin RNA expression

The RNA polymerase III (pol III) type III promoters U6 and 7SK are routinely used to express short hairpin RNA (shRNA) molecules from a DNA construct. In this study, we identified, characterised and compared the porcine 7SK promoter in porcine (homologous) and non-porcine (heterologous) derived cell lines. The porcine 7SK small nuclear RNA (snRNA) was identified by alignment with known sequences and further characterisation of the upstream regions determined the presence of typical RNA pol III sequence motifs. The porcine 7SK (po7SK) promoter was cloned and a one-step PCR strategy used to construct shRNA expression cassettes. The 7SK promoter activity was quantified by knockdown of the exogenous reporter gene encoding the enhanced green fluorescent protein (EGFP). Results indicated the po7SK promoter was functional in both homologous and heterologous cells lines. The identification and characterisation of the porcine RNA pol III promoter will contribute to the area of RNAi delivery and further develop our understanding of RNA promoter structure and function.

In vitro inhibition of classical swine fever virus replication by siRNAs targeting Npro and NS5B genes

Classical swine fever (CSF) is a highly contagious disease of pigs, which causes important economic losses worldwide. In the present study, the specific effect of RNA interference on the replication of CSF virus (CSFV) was explored. Three species of small interfering RNA (siRNA), targeting different regions of CSFV Npro and NS5B genes, were prepared by in vitro transcription. After transfection of PK-15 cells with each of the siRNAs followed by infection with CSFV, the viral proliferation within the cells was examined by indirect immunofluorescence microscopy. At 72 h post-infection, only a few siRNA-treated cells were positive for viral antigen staining, while most untreated virus-infected cells were positive. Treatment with the siRNAs caused a 4-12-fold reduction in viral genome copy number as assessed by real time RT-PCR. Transfection with the siRNAs also suppressed the production of infectious virus by up to 467-fold as assessed by TCID50 assay. These results suggested that the three species of siRNAs can efficiently inhibit CSFV genome replication and infectious virus production, with the inhibition persisting for 72-84 h.

Specific small interfering RNAs-mediated inhibition of replication of porcine encephalomyocarditis virus in BHK-21 cells

Encephalomyocarditis virus (EMCV) is recognized as a pathogen inducing acute myocarditis and sudden death in preweaned piglets and severe reproductive failure in sows. In this study, eight specific small interfering RNA (siRNA) duplexes targeting different genomic regions of EMCV BJC3 were designed and their ability to inhibit virus replication in BHK-21 cells was investigated. The results showed that BHK-21 cells transfected with siRNA duplexes to 2C gene (JH-4,666, BJC-1,739), 2B gene (BJC-807), 3C gene (BJC-2,363) and 3D gene (BJC-3269) were specifically resistant to EMCV infection when exposed to 500 times the 50% cell culture infective dose (CCID(50)) of EMCV. The levels of the 3D gene in the transfected cells were obviously decreased. IFA and Western blotting analysis confirmed that the expression of VP1 protein in cell culture transfected with the siRNAs was apparently reduced. Of the five siRNAs, JH-4,666, BJC-2,363 and BJC-3,269 were the most effective. Combination of the siRNA duplexes enhanced the inhibition of EMCV replication. Our data indicated that specific siRNAs are able to inhibit the replication of porcine encephalomyocarditis virus in BHK-21 cells, suggesting that RNAi might provide a new approach to prevent EMCV infection.