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Updated: Feb 27, 2026
Comprehensive Analysis of Procoagulant Platelets Exhibiting Features of Necrosis, Apoptosis and Platelet Activation
Published on: May 23, 2025
Temsirolimus Sensitive Stimulation of Platelet Activity, Apoptosis and Aggregation by Collagen Related Peptide
Hang Cao1, Rosi Bissinger1, Anja T Umbach1
1Department of Medicine III, Tuebingen, Germany.
Background/Aims:
The mammalian target of rapamycin (mTOR) inhibitor temsirolimus stimulates apoptosis of tumor cells and is thus therapeutically used for the treatment of diverse malignancies. On the other hand, temsirolimus has been shown to protect against apoptosis of hippocampal neurons. Similar to nucleated cells, blood platelets may enter suicidal death characterized by cell shrinkage and cell membrane scrambling. Platelet apoptosis is frequently preceded by Ca2+ entry, degranulation, integrin activation and stimulation of caspases. Those events could be triggered by collagen related peptide (CRP). The present study explored whether treatment of platelets with temsirolimus modifies platelet activation, caspase activity, platelet shrinkage, and phosphatidylserine abundance.
Methods:
Platelets isolated from wild-type mice were exposed for 30 minutes to temsirolimus (40 µg/ml) without or with additional CRP (2 µg/ ml or 5 µg/ml) treatment. Flow cytometry was employed to estimate cytosolic Ca2+-activity ([Ca2+]i) from Fluo-3 fuorescence, platelet degranulation from P-selectin abundance, integrin activation from αIIbβ3 integrin abundance, caspase activity utilizing an Active Caspase-3 Staining kit, phosphatidylserine abundance from annexin-V-binding and relative platelet volume from forward scatter.
Results:
In the absence of CRP, the administration of temsirolimus (40 µg/ml) significantly decreased [Ca2+]i, but did not significantly modify P-selectin abundance, activated αIIbβ3 integrin, annexin-V-binding, cell volume, caspase activity and aggregation. Exposure of platelets to CRP was followed by significant increase of [Ca2+]i, P-selectin abundance, αIIbβ3 integrin activity, annexin-V-binding, ROS, caspase activity and aggregation, effects significantly blunted in the presence of temsirolimus. CRP further decreased forward scatter, an effect again significantly blunted by temsirolimus.
Conclusions:
Temsirolimus is a powerful inhibitor of platelet activation and suicidal platelet death.
Insights
Temsirolimus inhibits platelet activation and suicidal death, even when triggered by collagen-related peptide (CRP). This mTOR inhibitor significantly blunts CRP-induced increases in calcium, degranulation, and caspase activity in platelets.
Area of Science:
- Pharmacology
- Hematology
- Cell Biology
Background:
- Temsirolimus, an mTOR inhibitor, treats malignancies but protects neurons from apoptosis.
- Platelets undergo apoptosis, characterized by shrinkage and membrane changes, often preceded by calcium influx, degranulation, and caspase activation.
- Collagen-related peptide (CRP) can trigger these platelet activation and apoptosis pathways.
Purpose of the Study:
- To investigate the effect of temsirolimus on platelet activation and apoptosis.
- To determine if temsirolimus modifies CRP-induced platelet responses, including calcium activity, degranulation, integrin activation, caspase activity, and phosphatidylserine exposure.
Main Methods:
- Mouse platelets were treated with temsirolimus, with or without CRP.
- Flow cytometry assessed intracellular calcium ([Ca2+]i), P-selectin (degranulation), activated αIIbβ3 integrin, active caspase-3, and phosphatidylserine (annexin-V binding).
- Platelet volume (forward scatter) was also measured.
Main Results:
- Temsirolimus alone decreased [Ca2+]i but did not affect other activation markers.
- CRP significantly increased [Ca2+]i, P-selectin, αIIbβ3 integrin activation, annexin-V binding, and caspase activity.
- Temsirolimus significantly blunted all CRP-induced platelet activation and apoptosis markers, including cell shrinkage.
Conclusions:
- Temsirolimus effectively inhibits platelet activation.
- Temsirolimus prevents suicidal platelet death induced by CRP.
- Temsirolimus demonstrates a potent inhibitory effect on platelet activation and apoptosis.
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