Influenza-Induced Oxidative Stress Sensitizes Lung Cells to Bacterial-Toxin-Mediated Necroptosis

Abstract

SUMMARY Pneumonias caused by influenza A virus (IAV) co- and secondary bacterial infections are characterized by their severity and high mortality rate. Previously, we have shown that bacterial 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. We observe that IAV synergistically sensitizes lung epithelial cells for PFT-mediated necroptosis in vitro and in murine models of Spn co-infection and secondary infection. Pharmacological induction of oxidative stress without virus sensitizes cells for PFT-mediated necroptosis. Antioxidant treatment or inhibition of necroptosis reduces disease severity during secondary bacterial infection. Our results advance our understanding on the molecular basis of co- and secondary bacterial infection to influenza and identify necroptosis inhibition and antioxidant therapy as potential intervention strategies.

Virus-Induced Changes of the Respiratory Tract Environment Promote Secondary Infections With Streptococcus pneumoniae

“…The role of ply in coinfection is controversial. Whereas the previous study suggests that ply contributes to mortality during coinfection, another study did not find any difference in a coinfection of wt and ply-lacking pneumococci (Gonzalez-Juarbe et al, 2020;Liu et al, 2020). However, these discrepancies can be due to variations in the coinfection model (such as C57BL/6 vs BALB/c mice and day 5 vs day 7 after virus infection) and the pneumococcal strains used (TIGR4 vs D39).…”

“…Higher NanA transcription in bacteria from influenza-dispersed biofilms (Pettigrew et al, 2014), higher bacterial loads in in vivo mouse models of colonization and otitis media, better adherence to epithelial cells in vitro (Wren et al, 2017) No effect of nanA deletion in a mouse pneumonia model (King et al, 2009) Enhanced bacterial load in presence of the main sialic acid transporter SatABC (+/-sialidases NanA and NanB) in a mouse pneumonia model (Siegel et al, 2014) Pneumococcal surface protein A PspA Increased virulence in a mouse pneumonia model (King and Harmsen, 2009), higher transcription in pneumococci isolated from influenza-dispersed biofilms (Pettigrew et al, 2014) High temperature requirement A HtrA Increased bacterial load in a mouse pneumonia model (Sender et al, 2020) Pneumolysin Ply Contributes to necroptosis and virulence in epithelial cells in vitro and in a mouse pneumonia model (Gonzalez-Juarbe et al, 2020) No effect on virulence in vitro and in vivo using CRISPRi-Seq (Liu et al, 2020) - (Sender et al, 2020) outgrowth in the LRT (Sender et al, 2020). We describe influenza-induced redox imbalances in the LRT to which pneumococci adapt by inducing the pneumococcal surface protease/chaperone high temperature requirement A (HtrA), that helps the bacteria to grow under oxidative stress condition in vitro and in vivo, and protects them from host-mediated opsonophagocytosis by maintaining capsular production (Sender et al, 2020).…”

“…Influenza-induced oxidative stress also promotes necroptosis caused by the pneumococcal cytotoxin, pneumolysin (ply) ( Gonzalez-Juarbe et al., 2020 ). Necroptosis is a form of regulated inflammatory cell death which can be induced by both influenza infection ( Nogusa et al., 2016 ) and the pore-forming toxin, ply, of pneumococci ( Gonzalez-Juarbe et al., 2015 ), resulting in release of molecules that enhance pro-inflammatory processes and viral clearance in the lungs, but can also disrupt immune homeostasis.…”

“…Necroptosis is a form of regulated inflammatory cell death which can be induced by both influenza infection ( Nogusa et al., 2016 ) and the pore-forming toxin, ply, of pneumococci ( Gonzalez-Juarbe et al., 2015 ), resulting in release of molecules that enhance pro-inflammatory processes and viral clearance in the lungs, but can also disrupt immune homeostasis. The study of Gonzalez-Juarbe et al., 2020 investigated the role of necroptosis during influenza-pneumococcal coinfection and in a series of experiments they show that influenza-induced necroptosis can be inhibited by antioxidant treatment, resulting in reduced disease severity and less tissue damage during secondary pneumococcal infection ( Gonzalez-Juarbe et al., 2020 ). A potential advantageous effect of antioxidant treatment for pneumococci themselves and pneumococcal growth, as observed in our study ( Sender et al., 2020 ), was not investigated in this study.…”

“…The inflammation-induced leakage that does not only lead to acute respiratory distress syndrome, but also provides nutrient for bacteria to feed on ( Sender et al., 2020 ), can be at least partly prevented by treatment with soluble ligands that reduce vascular permeability in the lungs and other organs and improve survival in animal models ( London et al., 2010 ). Systemic administration of antioxidants as immunomodulatory therapy to neutralize virus-induced oxidative stress and increase macrophage activity improves survival in influenza-pneumococci coinfected mice ( Wu et al., 2017 ; Gonzalez-Juarbe et al., 2020 ). However, antioxidant treatment may affect pneumococcal growth, as observed in our study ( Sender et al., 2020 ), but whether route, dose and time of antioxidant administration may affect disease outcome differently remains to be determined.…”