Influenza Virus Neuraminidase Engages CD83 and Promotes Pulmonary Injury

[Inhibitory effect of 5-hydroxy-6,7-dimethoxyflavone on H1N1 influenza virus-induced ferroptosis and inflammation in A549 cells and its possible mechanisms]

OBJECTIVE

To investigate the protective effect of 5-hydroxy-6,7-dimethoxyflavone (5-HDF), a compound extracted from Elsholtzia blanda Benth., against lung injury induced by H1N1 influenza virus and explore its possible mechanism of action.

METHODS

5-HDF was extracted from Elsholtzia blanda Benth. using ethanol reflux extraction and silica gel chromatography and characterized using NMR and MS analyses. In an A549 cell model of H1N1 influenza virus infection (MOI=0.1), the cytotoxicity of 5-HDF was assessed using MTT assay, and its effect on TRAIL and IL-8 expressions was examined using flow cytometry; Western blotting was used to detect the expression levels of inflammatory, apoptosis, and ferroptosis-related proteins. In a mouse model of H1N1 influenza virus infection established by nasal instillation of 50 μL H1N1 virus at the median lethal dose, the effects of 30 and 60 mg/kg 5-HDF by gavage on body weight, lung index, gross lung anatomy and lung histopathology were observed.

RESULTS

5-HDF exhibited no significant cytotoxicity in A549 cells within the concentration range of 0-200 μg/mL. In H1N1-infected A549 cells, treatment with 5-HDF effectively inhibited the activation of phospho-p38 MAPK and phospho-NF-κB p65, lowered the expressions of IL-8, enhanced the expression of anti-ferroptosis proteins (SLC7A11 and GPX4), and inhibited the expressions of apoptosis markers PARP and caspase-3 and the apoptotic factor TRAIL. In H1N1-infected mice, treatment with 5-HDF for 7 days significantly suppressed body weight loss and increment of lung index and obviously alleviated lung tissue pathologies.

CONCLUSION

5-HDF offers protection against H1N1 influenza virus infection in mice possibly by suppressing H1N1-induced ferroptosis, inflammatory responses, and apoptosis via upregulating SLC7A11 and GPX4, inhibiting the activation of phospho-NF-κB p65 and phospho-p38 MAPK, and decreasing the expression of cleaved caspase3 and cleaved PARP.

Mesenchymal stem cells ameliorate H9N2-induced acute lung injury by inhibiting caspase-3-GSDME-mediated pyroptosis of lung alveolar epithelial cells

Influenza A virus infection mediates the host's excessive immune response, wherein caspase-3-GSDME-mediated pyroptosis of lung alveolar epithelial cells can contribute to inducing cytokine storm, leading to acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Numerous studies have shown that mesenchymal stem cells (MSCs) possess potent immunomodulatory abilities and can mitigate virus-induced cytokine storm and lung injury. However, the role of MSCs in lung pyroptosis remains poorly understood. In this study, we established an ALI model using a mouse-adapted strain of avian influenza virus H9N2 (MA01) and intervened by injecting appropriate bone marrow-derived mesenchymal stem cells (BMMSCs) into the mouse's trachea. The results obtained from animal experiments demonstrated that BMMSCs prevented and ameliorated ALI by inhibiting Caspase-3-GSDME-mediated pyroptosis of lung epithelial cells as well as hypercytokinemia. Similarly, corresponding results were observed in vitro, where BMMSCs and the lung epithelial cell line MLE-12 cells were co-cultured in a transwell compartment. Additionally, the caspase-3 inhibitor Z-DEVD-FMK could block MA01-induced GSDME activation. Furthermore, by combining RNA-Seq data with in vitro and in vivo results, we also discovered that MA01-induced pyroptosis is associated with the BAK/BAX-dependent mitochondrial apoptosis pathway. Notably, BMMSCs exhibit the ability to interfere with this signaling pathway. In conclusion, this study provides novel theoretical support for the utilization of BMMSCs in the treatment of ALI induced by influenza.

Immune response in influenza virus infection and modulation of immune injury by viral neuraminidase

Influenza A viruses cause severe respiratory illnesses in humans and animals. Overreaction of the innate immune response to influenza virus infection results in hypercytokinemia, which is responsible for mortality and morbidity. The influenza A virus surface glycoprotein neuraminidase (NA) plays a vital role in viral attachment, entry, and virion release from infected cells. NA acts as a sialidase, which cleaves sialic acids from cell surface proteins and carbohydrate side chains on nascent virions. Here, we review progress in understanding the role of NA in modulating host immune response to influenza virus infection. We also discuss recent exciting findings targeting NA protein to interrupt influenza-induced immune injury.

Advances in deciphering the interactions between viral proteins of influenza A virus and host cellular proteins

Influenza A virus (IAV) poses a severe threat to the health of animals and humans. The genome of IAV consists of eight single-stranded negative-sense RNA segments, encoding ten essential proteins as well as certain accessory proteins. In the process of virus replication, amino acid substitutions continuously accumulate, and genetic reassortment between virus strains readily occurs. Due to this high genetic variability, new viruses that threaten animal and human health can emerge at any time. Therefore, the study on IAV has always been a focus of veterinary medicine and public health. The replication, pathogenesis, and transmission of IAV involve intricate interplay between the virus and host. On one hand, the entire replication cycle of IAV relies on numerous proviral host proteins that effectively allow the virus to adapt to its host and support its replication. On the other hand, some host proteins play restricting roles at different stages of the viral replication cycle. The mechanisms of interaction between viral proteins and host cellular proteins are currently receiving particular interest in IAV research. In this review, we briefly summarize the current advances in our understanding of the mechanisms by which host proteins affect virus replication, pathogenesis, or transmission by interacting with viral proteins. Such information about the interplay between IAV and host proteins could provide insights into how IAV causes disease and spreads, and might help support the development of antiviral drugs or therapeutic approaches.

Pandemic influenza A (H1N1) virus causes abortive infection of primary human T cells

Influenza A virus still represents a noticeable epidemic risk to international public health at present, despite the extensive use of vaccines and anti-viral drugs. In the fight against pathogens, the immune defence lines consisting of diverse lymphocytes are indispensable for humans. However, the role of virus infection of lymphocytes and subsequent abnormal immune cell death remains to be explored. Different T cell subpopulations have distinct characterizations and functions, and we reveal the high heterogeneity of susceptibility to viral infection and biological responses such as apoptosis in various CD4⁺ T and CD8⁺ T cell subsets through single-cell transcriptome analyses. Effector memory CD8⁺ T cells (CD8⁺ T_EM) that mediate protective memory are identified as the most susceptible subset to pandemic influenza A virus infection among primary human T cells. Non-productive infection is established in CD8⁺ T_EM and naïve CD8⁺ T cells, which indicate the mechanism of intracellular antiviral activities for inhibition of virus replication such as abnormal viral splicing efficiency, incomplete life cycles and up-regulation of interferon-stimulated genes in human T cells. These findings provide insights into understanding lymphopenia and the infectious mechanisms of pandemic influenza A virus and broad immune host–pathogen interactional atlas in primary human T cells.