As a zoonotic virus, Japanese Encephalitis virus (JEV) poses a serious threat to human health and the breeding industry. Regarding the mechanism and complications of tissue inflammation caused by JEV, such as encephalitis and orchitis, there is no effective drug treatment currently, and the mechanism of occurrence has not been thoroughly studied. Therefore, it is necessary to study the mechanism of the inflammatory pathway caused by JEV. As one of the key proteins regulating cell death, BCL2 antagonist/killer (BAK) is also a necessary prerequisite for the release of cellular inflammatory factors. We found that after JEV infection, BAK-knockdown cells died less than normal cells, and the transcription levels of inflammatory factors such as TNF, IFNα, and IL-1β and their corresponding regulatory genes were also significantly reduced. By further verifying protein expression on the cell death pathway, it was found that pyroptotic activation and virus titer were also significantly reduced in BAK.KD cells, suggesting that JEV proliferation might be related to BAK-induced cell death. From our data, we could conclude that JEV utilized the BAK-promoted pyroptotic pathway to release more virions after the final Gasdermin D-N (GSDMD-N) protein pore formation for the purpose of JEV proliferation. Therefore, the study of the endogenous cell death activator protein BAK and the final release pathway of JEV, is expected to provide some new theoretical basis for future research on the screening of targeted drugs for the treatment of inflammatory diseases caused by JEV.

(1) Background: Porcine Parvovirus (PPV) is a single-stranded DNA virus without envelope which causes great harm in relation to porcine reproductive disorders in clinic. Cluster of Differentiation 38 (CD38) is a transmembrane protein widely existing in mammals. Its various functions make it a very popular research object, including in the viral infection field. (2) Methods: Western blotting and an EdU Cell Proliferation Kit were used to evaluate the effect of CD38-deficient cells. Relative quantitative real-time RT-PCR was used to detect the transcription levels of cytokines after PPV infection. The renilla luciferase reporter gene assay was used to verify the activation function of CD38 on downstream factors. The fluorescence probe method was used to detect the level of intracellular reactive oxygen species (ROS). (3) Results: This study found that the loss of CD38 function inhibited the up-regulated state of Toll-like Receptor 9 (TLR9), Interferon-α (IFN-α), and Myxovirus Resistance 1 (Mx1) after PPV infection. The luminescence of the group transfected with both CD38 expression plasmid and TLR9 promoter renilla luciferase reporter plasmid was significantly up-regulated compared with the control, suggesting that CD38 may activate the promoter of TLR9. In addition, CD38 deficiency not only activated the transcription of Sirtuin-1 (SIRT1), but also inhibited ROS level and the transcription of NLR Family Pyrin Domain Containing 3 (NLRP3). (4) Conclusion: (i) CD38 may participate in the TLR9/IFN-α/Mx1 pathway by activating the expression of TLR9 after PPV infected PK-15 cells; (ii) CD38 may activate the NLRP3/CASP1 pathway by increasing ROS level; (iii) CD38 deficiency activates the expression of SIRT1 and can prevent the normal proliferation of PPV.

The manipulation of host cellular metabolism is a key strategy for flaviviruses like Japanese encephalitis virus (JEV) to establish a productive infection. This study identifies the host NADase CD38 as a central regulator of this process. Using a CRISPR/Cas9-generated CD38 knockout (KO) TM3 cell model, we found that CD38 deficiency significantly restricted the production of infectious viral particles. While loss of CD38 also partially impaired viral entry, our central finding is that CD38 primarily promotes JEV infection by suppressing a host-intrinsic metabolic defense. We show that CD38 deficiency leads to a surge in intracellular NAD+, which sustains SIRT1 activity and inactivates p53, thereby blocking the mitochondrial apoptosis required for viral propagation. The dominance of this metabolic axis was confirmed through bidirectional pharmacological interventions; while SIRT1 inhibition using EX527 restored JEV replication, SIRT1 activation using SRT1720 suppressed it in wild-type cells. Our work reveals that JEV hijacks the CD38-NAD+-SIRT1-p53 axis to overcome host metabolic defenses in reproductive cell models, establishing CD38 as a promising therapeutic target.

Japanese encephalitis virus (JEV) is an important flavivirus that causes zoonotic and arboviral diseases. Infection with JEV not only induces acute central nervous system (CNS) infectious diseases but also leads to reproductive disorders. Currently, research on the pathogenic mechanism of JEV has mainly focused on CNS inflammation caused by infection, while studies on the pathogenic mechanism of JEV targeting the reproductive system are relatively scarce. This study used TM3 cells as a model to investigate the regulatory role of the CD4 molecule in JEV infection, the STAT1 signaling pathway, and inflammatory factors. Firstly, we found that CD4 knockdown significantly inhibited JEV replication in TM3 cells. Further virus adsorption and internalization experiments confirmed that CD4 knockdown specifically impaired the early stages of JEV invasion into cells. Additionally, CD4 knockdown also drastically attenuated JEV infection-induced STAT1 phosphorylation (p-STAT1) and the production of downstream inflammatory factors. To distinguish whether CD4 affects p-STAT1 through an indirect effect of reduced viral load or its direct involvement in signal transduction, we performed experiments using RO8191, a specific agonist of the STAT1 signaling pathway. The results showed that RO8191 treatment increased the expression levels of p-STAT1 protein and inflammatory factor mRNA in both normal cells and CD4 knockdown cells, but the recovery amplitude in the CD4 knockdown group was significantly lower. In contrast, CD4 complementation significantly elevated the expression levels of p-STAT1 protein and inflammatory factor mRNA. In conclusion, this study demonstrates that the CD4 molecule positively regulates JEV proliferation in TM3 cells, while also modulating STAT1—a key factor in the STAT signaling pathway—and downstream inflammatory cytokines. Notably, this regulatory effect operates independently of viral replication. These findings provide a theoretical foundation for further elucidation of JEV pathogenic mechanisms and offer a scientific basis for the prevention and control of JEV.

Host lipid metabolism is a critical determinant of viral pathogenesis. Although the interferon-inducible cholesterol 25-hydroxylase (CH25H) typically acts as a broad-spectrum antiviral protein, its expression and regulatory patterns during Japanese Encephalitis Virus (JEV) infection display unique features. Here, we demonstrate that 25-hydroxycholesterol (25HC), the product of CH25H, potently inhibits JEV proliferation by suppressing SREBP2 activation. Distinct from the majority of viral infections that induce CH25H upregulation, JEV infection elicits a transient reduction in CH25H abundance immediately after infection, coupled with a persistent elevation in SREBP2 expression. This inverse correlation suggests that JEV actively suppresses the CH25H-mediated metabolic checkpoint to maintain a cholesterol-synthetic environment favorable for replication. By pharmacologically simulating the activity of 25HC, we further verify that targeting the SREBP2 signaling axis can efficiently counteract this virally induced metabolic reprogramming. Our study identifies CH25H downregulation and concomitant SREBP2 activation as a key metabolic signature of JEV pathogenesis.