Apoptotic Platelet Events Are Not Observed in Severe von Willebrand Disease-Type 2B Mutation p.V1316M

Area of Science:

• Hematology
• Molecular Biology
• Cell Biology

Background:

• Von Willebrand disease type 2B (VWD-2B) is characterized by thrombocytopenia and increased platelet clearance.
• This phenomenon was hypothesized to be caused by platelet apoptosis, triggered by the spontaneous binding of von Willebrand factor (VWF) to its receptor, glycoprotein Ib (GPIb).

Purpose of the Study:

• To investigate whether the VWF/p.V1316M mutation, a severe VWD-2B mutation causing spontaneous VWF-GPIb binding, induces platelet apoptosis.

Main Methods:

• Assessed apoptosis in platelets from two VWD-2B patients with the VWF/p.V1316M mutation and from a VWD-2B mouse model.
• Evaluated mitochondrial transmembrane depolarization, phosphatidylserine (PS) exposure (annexin-V staining), pro-apoptotic protein expression (Bak, Bax), and caspase-3 activity.

Main Results:

• Platelets from VWD-2B patients with VWF/p.V1316M showed no significant signs of apoptosis, including mitochondrial depolarization or substantial PS exposure.
• Pro-apoptotic protein levels and caspase-3 activity were comparable to control platelets.
• The VWD-2B mouse model expressing mVWF/p.V1316M did not exhibit increased apoptosis compared to controls expressing mVWF/WT.

Conclusions:

• The VWF/p.V1316M mutation, despite spontaneous VWF-GPIb binding, does not induce platelet apoptosis.
• Apoptosis is unlikely to be the underlying mechanism for thrombocytopenia in severe VWD-2B patients with this specific mutation.