Influenza-induced oxidative stress sensitizes lung cells to bacterial toxin-mediated necroptosis

Abstract

RationalePneumonia caused by Influenza A virus (IAV) co- and secondary bacterial infections are characterized by their severity. Previously we have shown that pore-forming toxin (PFT)-mediated necroptosis is a key driver of acute lung injury during bacterial pneumonia. Here, we evaluate the impact of IAV on PFT-induced acute lung injury during co- and secondary Streptococcus pneumoniae (Spn) infection.ObjectivesDetermine the impact of IAV infection on bacterial PFT-mediated lung epithelial cell (LEC) necroptosis. Determine the molecular basis for increased sensitivity and if inhibition of necroptosis or oxidative stress blocks IAV sensitization of LEC to PFT.MethodsMice and cells were challenged with IAV followed by Spn. Necroptosis was monitored by measuring cell death at fixed time points post-infection and immunofluorescent detection of necroptosis. Wildtype mice and LEC were treated with necroptosis inhibitors. Necroptosis effector molecule MLKL deficiency was tested for infection synergy. Oxidative damage to DNA and lipids as result of infection was measured in vitro and in vivo. Necroptosis and anti-oxidant therapy efficacy to reduce disease severity was tested in vivo.Measurements and Main ResultsIAV synergistically sensitized LEC for PFT-mediated necroptosis in vitro and in murine models of Spn co-infection and secondary infection. Pharmacological induction of oxidative stress sans virus sensitized cells for PFT-mediated necroptosis. Necroptosis inhibition reduced disease severity during secondary bacterial infection.ConclusionsIAV-induced oxidative stress sensitizes LEC for PFT-mediated necroptosis. This is a new molecular explanation for severe influenza-associated bacterial infections. Necroptosis inhibitors are potential therapeutic strategies to reduce IAV-primed bacterial pneumonia severity.SummaryHere we demonstrate that Influenza A virus (IAV) infection synergistically sensitizes lung cells to bacterial pore-forming toxin (PFT)-mediated necroptosis. Moreover, this contributes to the severity of lung injury that is observed during co- and secondary infection with Streptococcus pneumoniae. IAV-induced oxidative stress was identified as a key factor contributing to cell sensitization and induction of oxidative stress sans virus was sufficient to synergistically enhance susceptibility to PFT-mediated killing. Our results advance our understanding on the molecular basis of co- and secondary bacterial infection to influenza and identifies necroptosis inhibition and antioxidant therapy as potential intervention strategies.

Microbiota Modulating Nutritional Approaches to Countering the Effects of Viral Respiratory Infections Including SARS-CoV-2 through Promoting Metabolic and Immune Fitness with Probiotics and Plant Bioactives

“…Thus, NLR may be used as a prognostic factor for disease severity in VRIs that could facilitate an early detection of severity and the rapid implementation of interventions to aid patient responses to infection. Virus-induced oxidative stress via the generation of reactive oxygen species (ROS) is also a factor that increases the expression of proinflammatory cytokines and chemokines [31] and sensitizes lung cells to bacteria toxin-mediated necroptosis [32]. The heightened neutrophil influx and cytokine storm coupled with subsequent ARDS correlates with multi-organ damage and mortality among COVID-19 patients [28].…”

“…Lymphopenia, particularly in CD4+ and CD8+ Tcells, as well as reduced interferon (IFN)-γ production by CD4+ T-cells but not CD8+ T cells or natural killer cells are associated with the increased severity of COVID-19 [29]. CD4+ T-cells regulate the Virus-induced oxidative stress via the generation of reactive oxygen species (ROS) is also a factor that increases the expression of proinflammatory cytokines and chemokines [31] and sensitizes lung cells to bacteria toxin-mediated necroptosis [32]. The heightened neutrophil influx and cytokine storm coupled with subsequent ARDS correlates with multi-organ damage and mortality among COVID-19 patients [28].…”

“…The antiviral effects of polyphenols have been demonstrated to be mediated either by direct inhibitory effects on virus replication or through the induction of immunomodulatory/antioxidant responses [170,171]. Oxidative stress has been implicated in lung tissue injury and epithelial barrier dysfunction in acute respiratory viral infections [31,32]. Accumulating evidence has revealed the excellent immunomodulatory effects of epigallocatechin-3-gallate (EGCG), abundant in green tea on both innate and adaptive immune responses [173].…”

Examining the Executioners, Influenza Associated Secondary Bacterial Pneumonia

“…Continuous viral replication induces reactive oxygen species (ROS) generation from host cells. The presence of viral-induced ROS leads to an upregulation of the S. pneumoniae cytotoxin pneumolysin and causes enhanced necroptosis of the lung epithelium [70]. Taken together, these observations demonstrate a synergistic effect of S. pneumoniae growth and virulence with influenza infection.…”

“…There is substantial overlap regarding the broad effects of influenza infection on S. pneumoniae and S. aureus. Both organisms demonstrated enhanced dissemination into the lungs and upregulation of virulence genes during influenza infection [26,61,62,70]. Evidence suggests that immediately upon being trafficked into the LRT, S. aureus forms microaggregates in the crypts of the alveolar wall [71].…”