Staphylococcus aureus Panton-Valentine Leukocidin triggers an alternative NETosis process targeting mitochondria

Area of Science:

• Microbiology
• Immunology
• Cell Biology

Background:

• Panton-Valentine Leukocidin (PVL) is a Staphylococcus aureus toxin implicated in severe infections.
• The precise mechanism of PVL action, particularly its interaction with host cells, remains incompletely understood.
• Recent evidence questions PVL's role as a simple pore-forming toxin.

Purpose of the Study:

• To investigate the mechanism by which PVL induces Neutrophil Extracellular Trap formation (NETosis).
• To elucidate the specific cellular pathways and molecules involved in PVL-mediated NETosis.
• To differentiate PVL-induced NETosis from other known NETosis pathways.

Main Methods:

• In vitro immunolabeling of human neutrophils exposed to purified PVL.
• Analysis of cellular responses including chromatin ejection, oxidative burst, mitochondrial activity, and autophagy.
• Investigation of signaling pathways involving calcium channels, Myeloperoxidase, peptidyl arginine deiminases, and Src kinases.
• Pharmacological inhibition of specific cellular components (e.g., Allopurinol).

Main Results:

• PVL, but not HlgCB, induced NETosis characterized by chromatin ejection decorated with antimicrobial peptides.
• PVL-mediated NETosis occurred independently of the NADPH oxidase oxidative burst.
• PVL localized with mitochondria, enhanced mitochondrial reactive oxygen species production, and increased autophagy, though autophagy was not essential for NET ejection.
• NETosis was dependent on Ca2+-activated SK channels and Myeloperoxidase activity, and abolished by Allopurinol.
• Massive histone H3 citrullination occurred, but inhibition of peptidyl arginine deiminases did not prevent NET extrusion.
• PVL-induced NETosis did not involve Src kinases, indicating a distinct signaling pathway compared to NADPH oxidase-dependent NETosis.

Conclusions:

• PVL induces a unique form of NETosis in neutrophils.
• This PVL-driven NETosis pathway differs significantly from canonical pathways, particularly in its independence from Src kinases and the NADPH oxidase pathway.
• PVL-induced NETosis may represent a bacterial strategy to evade or disrupt the host immune response, facilitating Staphylococcus aureus dissemination.