TNF-α increases Staphylococcus aureus-induced death of human alveolar epithelial cell line A549 associated with RIP3-mediated necroptosis.

Aim: To explore the role of tumor necrosis factor-alpha (TNF-α) on Staphylococcus aureus-induced necroptosis in alveolar epithelial cells.

Main Methods: The A549 alveolar epithelial cell line was pretreated with small interfering RNA (siRNA) against receptor interacting protein-3 (RIP3) and then stimulated by S. aureus, where some cells were pretreated with TNF-α or TNF-α with anti-TNF-α antibody simultaneously. A549 cell death was assessed using lactate dehydrogenase (LDH) leakage and flow cytometry analyses. The protein expressions of RIP1, RIP3, cleaved caspase-1, and cleaved caspase-8 were analyzed by western blot.

Key Findings: S. aureus-induced LDH release was increased significantly by TNF-α. In addition, flow cytometry showed that TNF-α increased A549 cell apoptosis and necrosis in S. aureus-infected cell cultures. Levels of RIP3 and cleaved caspase-1 protein in A549 cells infected with S. aureus increased at 12 h post-infection, as shown by western blot. Significant additional increases in RIP3 expression were observed following the addition of TNF-α. Decreasing RIP3 levels by siRNA significantly suppressed the release of LDH induced by TNF-α and S. aureus. RIP3 siRNA also significantly suppressed A549 cell necrosis induced by S. aureus and TNF-α at 6 and 12 h post-infection as shown by flow cytometry analysis.

Significance: TNF-α enhances the damage of S. aureus on lung epithelial cells, and its mechanism is associated with RIP3 mediated necroptosis.