Cathepsin G activates protease-activated receptor-4 in human platelets

Area of Science:

• Hematology
• Molecular Biology
• Immunology

Background:

• Protease-activated receptors (PARs) are key mediators of platelet signaling.
• PAR1 and PAR4 are expressed on human platelets, but their distinct roles remain unclear.
• Neutrophil cathepsin G induces platelet activation, but its receptor is unidentified.

Purpose of the Study:

• To determine the specific protease-activated receptor (PAR) involved in platelet activation by cathepsin G.
• To investigate the role of PAR4 in mediating platelet responses to neutrophil-derived proteases.
• To elucidate the mechanism of neutrophil-platelet interactions in inflammation.

Main Methods:

• Utilized PAR4-transfected cells and Xenopus oocytes to assess cathepsin G signaling.
• Employed functional assays on washed human platelets, including calcium mobilization and aggregation.
• Used specific antibodies against PAR4 and PAR1, and desensitization techniques to block receptor activity.
• Investigated neutrophil-dependent platelet activation using fMet-Leu-Phe stimulation.

Main Results:

• Cathepsin G induced calcium mobilization in PAR4-expressing systems and human platelets.
• An antibody targeting the PAR4 cleavage site blocked cathepsin G-induced platelet activation.
• PAR1 inhibition did not affect platelet responses to cathepsin G.
• Neutrophil-mediated platelet activation was abrogated by the PAR4 antibody.

Conclusions:

• Platelet responses to cathepsin G are primarily mediated by PAR4, not PAR1.
• PAR4 plays a critical role in platelet activation by neutrophil proteases.
• Cathepsin G may facilitate neutrophil-platelet interactions at sites of vascular injury or inflammation.