Stimulation of platelet apoptosis by peptidoglycan from Staphylococcus aureus 113

Area of Science:

• Immunology
• Cell Biology
• Microbiology

Background:

• Peptidoglycan (PGN), a bacterial cell wall component and microbe-associated molecular pattern (MAMP), triggers host immune responses.
• Bacterial infections can lead to platelet activation and thrombocytopenia, impacting disease pathophysiology.
• Previous studies indicate PGN can induce apoptosis in various host cells.

Purpose of the Study:

• To investigate whether purified peptidoglycan (PGN) fractions from Staphylococcus aureus induce apoptosis in blood platelets.
• To elucidate the specific cellular mechanisms involved in PGN-induced platelet apoptosis.

Main Methods:

• Platelets were exposed to HPLC-purified PGN fractions from Staphylococcus aureus.
• Annexin-V binding, DiOC6 fluorescence, Fluo-3AM staining, and immunofluorescence for active caspase-3 were used to assess platelet apoptosis markers.
• TLR-2 blocking antibodies and pancaspase inhibitor zVAD-FMK were employed to investigate signaling pathways.

Main Results:

• Exposure to monomeric PGN (mPGN) induced platelet apoptosis, evidenced by annexin-V binding, increased intracellular calcium ([Ca(2+)](i)), and mitochondrial depolarization.
• Caspase-3 activation and integrin α(IIb)β(3) upregulation were observed following mPGN exposure.
• TLR-2 antibodies, absence of extracellular calcium, and zVAD-FMK significantly inhibited mPGN-induced annexin-V binding.

Conclusions:

• Peptidoglycan (PGN) triggers platelet apoptosis in an activation-dependent manner.
• The process is characterized by mitochondrial depolarization, caspase-3 activation, and cell membrane scrambling, mediated through TLR-2.
• These findings highlight a novel mechanism by which bacterial components can affect platelet function during infection.