Rabies viruses of different virulence regulates inflammatory responses both in vivo and in vitro via MAPK and NF-κB pathway

Identification of key proteins of cytopathic biotype bovine viral diarrhoea virus involved in activating NF-κB pathway in BVDV-induced inflammatory response

Bovine viral diarrhoea virus (BVDV) is the etiologic agent of bovine viral diarrhea-mucosal disease, one of the most important viral diseases in cattle, with inflammatory diarrhea, enteritis, and mucosa necrosis as the major clinical manifestations. NF-κB is an important transcription complex that regulates the expression of genes involved in inflammation and immune responses. NLRP3 inflammasome plays a key role in the development of inflammatory diseases. However, whether the activation of NF-κB is crucial for BVDV infection-induced inflammatory responses remains unclear. The results of our present study showed that BVDV infection significantly activated the NF-κB pathway and promoted the expression of NLRP3 inflammasome components (NLRP3, ASC, pro-caspase 1) as well inflammatory cytokine pro-IL-1β in BVDV-infected bovine cells, resulting in the cleavage of pro-caspase 1 and pro-IL-1β into active form caspase 1 and IL-1β. However, the levels of the NLRP3 inflammasome components and inflammatory cytokines were obviously inhibited, as well the cleavage of pro-caspase 1 and pro-IL-1β in the pre-treated bovine cells with NF-κB-specific inhibitors after BVDV infection. Further, cytopathic biotype BVDV (cpBVDV) Erns and NS5A proteins with their key functional domains contributed to BVDV-induced inflammatory responses via activating the NF-κB pathway were confirmed experimentally. Especially, the NS5A can promote cholesterol synthesis and accelerate its augmentation, further activating the NF-κB signalling pathway. Conclusively, our data elucidate that the activation of NF-κB signaling pathway plays a crucial role in cpBVDV infection-induced inflammatory responses.

Gut Microbiota-Derived PGF2α Fights against Radiation-Induced Lung Toxicity through the MAPK/NF-κB Pathway

Radiation pneumonia is a common and intractable side effect associated with radiotherapy for chest cancer and involves oxidative stress damage and inflammation, prematurely halting the remedy and reducing the life quality of patients. However, the therapeutic options for the complication have yielded disappointing results in clinical application. Here, we report an effective avenue for fighting against radiation pneumonia. Faecal microbiota transplantation (FMT) reduced radiation pneumonia, scavenged oxidative stress and improved lung function in mouse models. Local chest irradiation shifted the gut bacterial taxonomic proportions, which were preserved by FMT. The level of gut microbiota-derived PGF2α decreased following irradiation but increased after FMT. Experimental mice with PGF2α replenishment, via an oral route, exhibited accumulated PGF2α in faecal pellets, peripheral blood and lung tissues, resulting in the attenuation of inflammatory status of the lung and amelioration of lung respiratory function following local chest irradiation. PGF2α activated the FP/MAPK/NF-κB axis to promote cell proliferation and inhibit apoptosis with radiation challenge; silencing MAPK attenuated the protective effect of PGF2α on radiation-challenged lung cells. Together, our findings pave the way for the clinical treatment of radiotherapy-associated complications and underpin PGF2α as a gut microbiota-produced metabolite.

Comprehensive analysis of protein acetylation and glucose metabolism inmouse brains infected with rabies virus

Rabies, caused by rabies virus (RABV), is a widespread zoonosis that is nearly 100% fatal. Alteration of the metabolic environment affects viral replication and the immune response during viral infection. In this study, glucose uptake was increased in mouse brains at the late stage of infection with different RABV strains (lab-attenuated CVS strain and wild-type DRV strain). To illustrate the mechanism underlying glucose metabolism alteration, comprehensive analysis of lysine acetylation and target analysis of energy metabolites in mouse brains infected with CVS and DRV strains were performed. A total of 156 acetylated sites and 115 acetylated proteins were identified as significantly different during RABV infection. Compared to CVS- and mock-infected mice, the lysine acetylation levels of glycolysis and tricarboxylic acid (TCA) cycle enzymes were decreased, and enzyme activity was upregulated in DRV-infected mouse brains. Metabolomic analysis revealed that high levels of oxaloacetate (OAA) in RABV-infected mouse brains. Specifically, the OAA level in CVS-infected mouse brains was higher than that in DRV-infected mouse brains, which contributed to the enhancement of the metabolic rate at the substrate level. Finally, we confirmed that OAA could reduce excessive neuroinflammation in CVS-infected mouse brains by inhibiting JNK and P38 phosphorylation. Taken together, this study provides fresh insight into the different strategies the host adapts to regulate glucose metabolism for energy requirements after different RABV strain infection and suggest that OAA treatment could be a potential strategy to prevent neural damage during RABV infection. IMPORTANCE Both viral replication and the host immune response are highly energy-dependent. It is important to understand how the rabies virus affects energy metabolism in the brain. Glucose is the direct energy source for cell metabolism. Previous studies have revealed that there is some association between acetylation and metabolic processes. In this study, comprehensive protein acetylation and glucose metabolism analysis were conducted to compare glucose metabolism in mouse brains infected with different RABV strains. Our study demonstrates that the regulation of enzyme activity by acetylation and OAA accumulation at the substrate level are two strategies for the host to respond to the energy requirements after RABV infection. Our study also indicates the potential role OAA could play in neuronal protection by suppressing excessive neuroinflammation.

Innate Immune Signaling and Role of Glial Cells in Herpes Simplex Virus- and Rabies Virus-Induced Encephalitis

The environment of the central nervous system (CNS) represents a double-edged sword in the context of viral infections. On the one hand, the infectious route for viral pathogens is restricted via neuroprotective barriers; on the other hand, viruses benefit from the immunologically quiescent neural environment after CNS entry. Both the herpes simplex virus (HSV) and the rabies virus (RABV) bypass the neuroprotective blood-brain barrier (BBB) and successfully enter the CNS parenchyma via nerve endings. Despite the differences in the molecular nature of both viruses, each virus uses retrograde transport along peripheral nerves to reach the human CNS. Once inside the CNS parenchyma, HSV infection results in severe acute inflammation, necrosis, and hemorrhaging, while RABV preserves the intact neuronal network by inhibiting apoptosis and limiting inflammation. During RABV neuroinvasion, surveilling glial cells fail to generate a sufficient type I interferon (IFN) response, enabling RABV to replicate undetected, ultimately leading to its fatal outcome. To date, we do not fully understand the molecular mechanisms underlying the activation or suppression of the host inflammatory responses of surveilling glial cells, which present important pathways shaping viral pathogenesis and clinical outcome in viral encephalitis. Here, we compare the innate immune responses of glial cells in RABV- and HSV-infected CNS, highlighting different viral strategies of neuroprotection or Neuroinflamm. in the context of viral encephalitis.