The expression loss of GPIbα due to ectodomain shedding in PRP derived platelet concentrates during storage

Platelet adhesion typically occurs by the critical role of GPIb-V-IX in capturing free-flowing platelets to the injured vessel wall where its rapid binding kinetics enables platelet tethering even under conditions of high shear through the interaction of the major ligand-binding subunit of GPIb-V-IX, GPIbα with subendothelial-bound vWF. During storage, platelet undesired activation may lead to platelet storage lesion (PSL) which changes the expression levels of platelet functional receptors including GPIbα. This study investigates the levels of expression and ectodomain shedding of platelet adhesive receptor GPIbα during the storage of platelet rich plasma (PRP) concentrates (PRP- PCs).
Five PRP-platelet concentrates were obtained from Iranian Blood Transfusion Organization (IBTO). The GPIbα expressions of platelets were analyzed on day 1, 3 and 5 after storage using flowcytometry. To examine the ectodomain shedding of this receptor the microparticle free supernatants obtained from stored platelets were subjected to western blot analysis. For control study, blood specimens was drawn from healthy consenting individuals and resting platelets were isolated while resuspended in Tyrode buffer.
Our results indicated a continuous decrease of GPIbα expression during storage where the expression from fist day (Mean fluorescence intensity=86±5.9) was significantly reduced compared to that of fifth day (mean fluorescence intensity=61±7.7) after storage (P=0.0094). Conversely, shed GPIbα (Glycocalicin) demonstrated continuous elevation during five-day storage (P=0.0098). According to the results the shedding levels for the first day were increased from 0.31± 0.3 to 1.5± 0.4 by the day 5 after storage.
Our study has demonstrated significant loss of platelet GPIbα during storage mostly due to receptor ectodomain shedding that leads to significant increase of soluble GPIbα in stored platelets. Considering the high levels of shed GPIbα in long stored platelets whether the transfusion of such products might be associated with defective adhesive function of platelets or possible proinflammatory effects could be of interests for future investigation.