The relationship between autophagy and apoptosis during pseudorabies virus infection

Evaluation of the activity and mechanisms of oregano essential oil against PRV in vivo and in vitro

BACKGROUND

The Pseudorabies Virus (PRV) leading to pseudorabies and causes huge economic losses in pig industry. The development of novel PRV variations has diminished the efficacy of traditional vaccinations, and there is yet no medication that can stop the spread of PRV infection. Therefore, PRV eradication is challenging. Oregano essential oil, the plant-based ingredient for medication feed have been shown to has strong anti-herpesvirus activity, but no anti-PRV function has been reported.

RESULTS

The current study assessed the anti-pseudorabies virus (PRV) activity of oregano essential oil and explored its mechanisms and most effective components against PRV. Our in vivo findings demonstrated that oregano essential oil could decrease the PRV load in tissues, mitigate tissue lesions, and enhance the survival rate of mice. The potential antiviral mechanism involves augmenting humoral and cellular immune responses in PRV-infected mice. To further investigate the most effective components of oregano essential oil against PRV, an in vitro study was conducted, revealing that oregano essential oil and its main constituents, carvacrol and thymol, all diminished PRV intracellular proliferation in vitro. Carvacrol exhibited the most potent anti-PRV effect, serving as the primary contributor to oregano essential oil's anti-PRV activity. The mechanisms underlying carvacrol's anti-PRV properties include the upregulation of cytokines TNF-α, IFN-β, IFN-γ, IL-12, and the inhibition of PRV-induced apoptosis in BHK-21 cells.

CONCLUSIONS

Our study provides an effective drug for the prevention and control of PRV infection.

Pseudorabies virus gM and its homologous proteins in herpesviruses induce mitochondria-related apoptosis involved in viral pathogenicity

Apoptosis is a critical host antiviral defense mechanism. But many viruses have evolved multiple strategies to manipulate apoptosis and escape host antiviral immune responses. Herpesvirus infection regulated apoptosis; however, the underlying molecular mechanisms have not yet been fully elucidated. Hence, the present study aimed to study the relationship between herpesvirus infection and apoptosis in vitro and in vivo using the pseudorabies virus (PRV) as the model virus. We found that mitochondria-dependent apoptosis was induced by PRV gM, a late protein encoded by PRV UL10, a virulence-related gene involved in enhancing PRV pathogenicity. Mechanistically, gM competitively combines with BCL-XL to disrupt the BCL-XL-BAK complex, resulting in BCL-2-antagonistic killer (BAK) oligomerization and BCL-2-associated X (BAX) activation, which destroys the mitochondrial membrane potential and activates caspase-3/7 to trigger apoptosis. Interestingly, similar apoptotic mechanisms were observed in other herpesviruses (Herpes Simplex Virus-1 [HSV-1], human cytomegalovirus [HCMV], Equine herpesvirus-1 [EHV-1], and varicella-zoster virus [VZV]) driven by PRV gM homologs. Compared with their parental viruses, the pathogenicity of PRV-ΔUL10 or HSV-1-ΔUL10 in mice was reduced with lower apoptosis and viral replication, illustrating that UL10 is a key virulence-related gene in PRV and HSV-1. Consistently, caspase-3 deletion also diminished the replication and pathogenicity of PRV and HSV-1 in vitro and in mice, suggesting that caspase-3-mediated apoptosis is closely related to the replication and pathogenicity of PRV and HSV-1. Overall, our findings firstly reveal the mechanism by which PRV gM and its homologs in several herpesviruses regulate apoptosis to enhance the viral replication and pathogenicity, and the relationship between gM-mediated apoptosis and herpesvirus pathogenicity suggests a promising approach for developing attenuated live vaccines and therapy for herpesvirus-related diseases.

Pseudorabies virus causes splenic injury via inducing oxidative stress and apoptosis related factors in mice

Pseudorabies virus (PRV) is an immunosuppressive virus that causes significant damage to the pig industry. This study aimed to investigate the effects of PRV on oxidative stress and apoptotic related in the spleen of mice to provide basis knowledge for further research on the pathogenesis of PRV in mice model. 36 mice were randomly two groups, the control group which only received 200 μL PBS and infection group which was subcutaneously infected with 200 μL of 1 × 103 TCID50/100 μL PRV, respectively. Spleen tissues in each group were collected for further experiments at 48, 72, and 96 h post-infection (hpi). Pathological observation was performed by hematoxylin and eosin Y staining. Biochemical and Flow cytometry methods were used to determine the reactive oxygen species profile and apoptosis of the spleen post-infection and apoptosis detection. In addition, q-PCR and Western blot were adopted to measure the apoptotic conditions of the spleen infected with PRV. The results indicated that the reactive oxygen species (ROS) level in the PRV infection group was remarkedly increased (p < 0.01) at a time-dependent pattern. Furthermore, the Malondialdehyde levels in the spleen of mice in the infection group increased (p < 0.01) in a time-dependent mode. However, the activity of Catalase, Superoxide dismutase, and glutathione peroxidase and the content of Glutathione in the infection group were decreased with the control group (p < 0.01) at a time-dependent manner. In addition, the ratio of splenocyte apoptosis in the infection group significantly increased (p < 0.01) in a time-dependent manner. In conclusion, PRV infection causes apoptosis of the spleen via oxidative stress in mice.

Apoptosis is mediated by FeHV-1 through the intrinsic pathway and interacts with the autophagic process

BACKGROUND

Although FeHV-1 is a primary feline pathogen, little is known about its interactions with host cells. Its relationship with several cellular pathways has recently been described, whereas its interplay with the apoptotic process, unlike other herpesviruses, has not yet been clarified. The aim of this work was to evaluate whether FeHV-1 induces apoptosis in its permissive cells, as well as the pathway involved and the effects of induction and inhibition of apoptosis on viral replication.

METHODS

Monolayers of CRFK cells were infected at different times with different viral doses. A cytofluorimetric approach allowed the quantification of cells in early and late apoptosis. All infections and related controls were also subjected to Western blot analysis to assess the expression of apoptotic markers (caspase 3-8-9, Bcl-2, Bcl-xL, NF-κB). An inhibitor (Z-VAD-FMK) and an inducer (ionomycin) were used to evaluate the role of apoptosis in viral replication. Finally, the expression of autophagy markers during the apoptosis inhibition/induction and the expression of apoptosis markers during autophagy inhibition/induction were evaluated to highlight any crosstalk between the two pathways.

RESULTS

FeHV-1 triggered apoptosis in a time- and dose-dependent manner. Caspase 3 cleavage was evident 48 h after infection, indicating the completeness of the process at this stage. While caspase 8 was not involved, caspase 9 cleavage started 24 h post-infection. The expression of other mitochondrial damage markers also changed, suggesting that apoptosis was induced via the intrinsic pathway. NF- κB was up-regulated at 12 h, followed by a gradual decrease in levels up to 72 h. The effects of apoptosis inhibitors and inducers on viral replication and autophagy were also investigated. Inhibition of caspases resulted in an increase in viral glycoprotein expression, higher titers, and enhanced autophagy, whereas induction of apoptosis resulted in a decrease in viral protein expression, lower viral titer, and attenuated autophagy. On the other hand, the induction of autophagy reduced the cleavage of caspase 3.

CONCLUSIONS

In this study, we established how FeHV-1 induces the apoptotic process, contributing to the understanding of the relationship between FeHV-1 and this pathway.