The glycoprotein Ibα–von Willebrand factor interaction induces platelet apoptosis

Abstract

Summary. Background: The interaction of glycoprotein (GP) Iba with von Willebrand factor (VWF) initiates platelet adhesion, and simultaneously triggers intracellular signaling cascades leading to platelet aggregation and thrombus formation. Some of the signaling events are similar to those occurring during apoptosis, however, it is still unclear whether platelet apoptosis is induced by the GPIba-VWF interaction. Objectives: To investigate whether the GPIba-VWF interaction induces platelet apoptosis and the role of 14-3-3f in apoptotic signaling. Methods: Apoptotic events were assessed in platelets or Chinese hamster ovary (CHO) cells expressing wild-type (1b9) or mutant GPIb-IX interacting with VWF by flow cytometry or western blotting. Results: Ristocetin-induced GPIba-VWF interaction elicited apoptotic events in platelets, including phosphatidylserine exposure, elevations of Bax and Bak, gelsolin cleavage, and depolarization of mitochondrial inner transmembrane potential. Apoptotic events were also elicited in platelets exposed to pathologic shear stresses in the presence of VWF; however, the shear-induced apoptosis was eliminated by the anti-GPIba antibody AK2. Furthermore, apoptotic events occurred in 1b9 cells stimulated with VWF and ristocetin, but were significantly diminished in two CHO cell lines expressing mutant GPIb-IX with GPIba truncated at residue 551 or a serine-to-alanine mutation at the 14-3-3f-binding site in GPIba. Conclusions: This study demonstrates that the GPIba-VWF interaction induces apoptotic events in platelets, and that the association of 14-3-3f with the cytoplasmic domain of GPIba is essential for apoptotic signaling. This finding may suggest a novel mechanism for platelet clearance or some thrombocytopenic diseases.

Protein kinase A determines platelet life span and survival by regulating apoptosis

“…Next, we investigated the role of PKA in platelet apoptosis. As previously reported, platelet apoptosis is a mitochondria-mediated intrinsic form of programmed cell death (6,7). Upon apoptotic stimulation, BCL-2 family proteins interact with the mitochondrial outer membrane, leading to transmembrane potential (ΔΨ m ) depolarization as well as activation of caspases (27,28).…”

“…Accumulating evidence indicates that the intrinsic program for apoptosis results in platelet destruction under pathological and physiological conditions (6,7). Similarly to eukaryotic cells, BAK and BAX are the 2 fated killers for those platelets that are not consumed during thrombosis and hemostasis (6,8,9).…”

Hemoglobin interaction with GP1b induces platelet activation and apoptosis: a novel mechanism associated with intravascular hemolysis

“…The Hb-GP1bα interaction stimulated the intrinsic (mitochondria-dependent) pathway of apoptotic signals (Figure 4), as other studies have demonstrated for VWF-GP1bα interactionmediated apoptosis in platelets. 33,34 In fact, the Hb-GP1bα interactions stimulated the activation of proapoptotic proteins Bak and Bax, release of apoptogenic cytochrome c from mitochondrial intermembrane space to the cytosol, and the activation of caspase-9 and caspase-3 ( Figure 4B and Online Supplementary Figure S10). The Hb-mediated apoptotic responses in turn induced the cytoskeleton expression of PS in platelets ( Figure 4A) and generation of platelet microparticles ( Figure 1C) as described in other agonists (such as thrombin, collagen, or ristocetin) that induced signal transduction.…”

Quinine-induced thrombocytopenia: drug-dependent GPIb/IX antibodies inhibit megakaryocyte and proplatelet production in vitro

“…29 Moreover, the GPIb/IX complex, through its association with the signaling protein 14-3-3, has been implicated in the induction of platelet apoptosis on VWF binding. 30 An analogous process may account for the induction of apoptosis in Mks on association of QITP antibodies with the GPIb/IX complex.…”