Platelets express adaptor proteins of the extrinsic apoptosis pathway and can activate caspase-8

Abstract

Background Apoptotic pathways in platelets are important for their survival and function. Platelet apoptosis may be involved in the pathogenesis of immune thrombocytopenia (ITP), an autoimmune-mediated disease. In contrast to the intrinsic apoptosis pathway, not much is known about the extrinsic pathway mechanisms in platelets. Objectives To investigate the expression of proteins involved in the extrinsic apoptosis pathway, including the death receptors, adaptor and regulator proteins in human platelets. To determine a possible trigger of the extrinsic apoptosis pathway in platelets. Methods To investigate the expression of key markers of the extrinsic pathway we used targeted immunofluorescence and flow cytometry assays. To study their expression and interaction we performed Western blotting and co-immunoprecipitation. Treated platelets with different apoptosis triggers were subjected to flow cytometry. Results We could identify the protein expression of the pro-apoptotic proteins TRADD (Tumor Necrosis Factor Receptor type 1- Associated DEATH Domain protein), TRAF2/5, (TNF Associated Factor) and DEDAF (Death Effector Domain- Associated Factor), FADD (Fas-Associated protein with death domain) as well as the anti-apoptotic proteins DJ-1 (Deglycase 1) and c-FLIP in human platelets. ABT-737 treatment induced a disruption in the co-localization of DJ-1 with FADD. Platelets treated with ABT-737 showed an activation in caspase-3 and -8. The exposure to TNF (Tumor Necrosis Factor), FasL (Fas ligand), and TWEAK or to plasma derived from ITP patients, did not lead to changes in caspase-3 and -8 activation in platelets. Conclusions Human platelets express some proteins of the extrinsic apoptosis pathway which can be modulated only by ABT-737 treatment. However so far, no other apoptosis trigger or interaction with an external receptor have been yet identified.

Preliminary Study on Apoptotic Proteins in Platelet from Adult Patients with Chronic Immune Thrombocytopenic Purpura

“…Goette et al [8] studied a cohort of adult ITP patients and found that increased platelet apoptosis involves loss of mitochondrial membrane potential (ΔΨm), caspase-3 activation, and phosphatidylserine externalization. Goelz et al [9] reported that TRADD (tumor necrosis factor re- [10]. In order to reveal the pathophysiological mechanism of chronic ITP and provide an experimental basis for new clinical treatment of chronic ITP, some proteins that had been studied in patients with chronic ITP are validated in our work and also new proteins were observed.…”

“…Goette et al [8] studied a cohort of adult ITP patients and found that increased platelet apoptosis involves loss of mitochondrial membrane potential (ΔΨm), caspase-3 activation, and phosphatidylserine externalization. Goelz et al [9] reported that TRADD (tumor necrosis factor receptor type 1-associated death domain protein), TRAF (TNF receptor-associated factor), DEDAF (death effector domain-associated factor), and FADD (Fas-associated death domain) as well as anti-apoptotic proteins DJ-1 (deglycase 1) and c-FLIP are proapoptotic proteins in human platelets. Another study indicated that platelet mitochondrial membrane depolarization, surface-exposed PS, high expression level of Bak and Bax, and low expression level of Bcl-xL contribute to the enhancement of platelet apoptosis [10].…”

Antitumor Activity of Palladium(II) Complexes on DU-145 Cell Line in Vitro

“…The intrinsic pathway is activated when an injury is inside the cell and the following stress activates the intrinsic pathway of apoptosis via mitochondria and the endoplasmic reticulum (30)(31)(32). The extrinsic pathway starts outside a cell when conditions in the extracellular environment determine that a cell must enter the process of apoptosis (32,33). Our previously defined results showed that Pd(II) complexes (C1-C5) exhibited cytotoxicity against DU-145 cancer cells by induction of apoptosis.…”

Platelet Innate Immune Receptors and TLRs: A Double-Edged Sword

“…In addition, human platelets were found to express some classical apoptosis receptors [ 45 ] and adaptor proteins, including tumor necrosis factor (TNF)-associated factor (TRAF)-2/5, Fas-associated protein with death domain (FADD), and death effector domain-associated factor (DEDAF) [ 46 ]. Interestingly, treating platelets with ligands of the receptors involved in extrinsic apoptosis pathways, such as TNF, Fas Ligand, and TWEAK, did not induce caspase 3/7 activation or PS exposure in this study, suggesting different triggering machinery for the extrinsic pathway.…”