Down-regulation of platelet adhesion receptors is a controlling mechanism of thrombosis, while also affecting post-transfusion efficacy of stored platelets

Abstract

Physiologically, upon platelet activation, uncontrolled propagation of thrombosis is prevented by regulating mechanisms which affect the expression and function of either platelet adhesion receptors or integrins. Receptor ectodomain shedding is an elective mechanism which is mainly involved in down-regulation of adhesion receptors GPIbα and GPVI. Platelet integrin αIIbβ3 can also be modulated with a calpain-dependent proteolytic cleavage. In addition, activating signals may induce the internalization of expressed receptors to selectively down-regulate their intensity. Alternatively, further activation of platelets is associated with microvesiculation as a none-selective mechanism which leads to the loss of membrane- bearing receptors. In a non-physiological condition, the storage of therapeutic platelets has also shown to be associated with the unwilling activation of platelets which triggers receptors down-regulation via aforementioned different mechanisms. Notably, herein the changes are time-dependent and not controllable. While the expression and shedding of pro-inflammatory molecules can induce post-transfusion adverse effects, stored-dependent loss of adhesion receptors by ectodomain shedding or microvesiculation may attenuate post-transfusion adhesive functions of platelets causing their premature clearance from circulation. In its first part, the review presented here aims to describe the mechanisms involved in down-regulation of platelet adhesion receptors. It then highlights the crucial role of ectodomain shedding and microvesiculation in the propagation of “platelet storage lesion” which may affect the post-transfusion efficacy of platelet components.

Collagen-dependent platelet dysfunction and its relevance to either mitochondrial ROS or cytosolic superoxide generation: a question about the quality and functional competence of long-stored platelets

“…In addition, we already showed that total adhesion of platelets to collagen is reversely correlated to GPVI shedding [11]. However, it seems that the evaluation of platelet spreading on collagen provides more information about the platelet signaling competence and functional quality beyond that seen for the simple adhesion [50].In addition, since platelet rm adhesion and spreading is mainly mediated by GPVI receptor [1], platelets adhesion area seems to be a better indicator of GPVI competence rather than simple adhesion which might be also modulated by other less important receptors or be affected by artifacts. As presented here, in 5 daysstored PCs, the reduction of platelet spreading on collagen (calculated by platelet surface area) is much more signi cant than simple adhesion loss during storage.…”

“…CCCP also showed to signi cantly promote GPVI shedding by ADAM17 rather than ADAM10 which is considered to be the speci c sheddase for GPVI. Given the fact that ADAM 17 activity is modulated by ROS generation [1], the CCCP induced shedding might be also affected by oxidant pathways. Based on these background studies here, for the rst time we showed CCCP-induced ROS generation in platelets that makes a direct link between platelet mitochondrial lesion and induced oxidative stress in an experimental setup.…”

“…Several line of evidence indicated that a well-tuned physiologic concentration of ROS can act as an important modulator of platelets adhesive capacity. However, as a general rule, the oxidant stress induced by unleashed accumulation of ROS in platelets can seriously affect adhesion receptors shedding and their function [1].…”

“…However, notably this is the engagement of platelet GPVI receptor and collagen that mainly supports platelet rm adhesion and spreading to the site of vascular injury [1,2]. GPVI ligation to collagen also induces potent inside out signals which play important roles in the enhancement of integrin activation leading to platelet aggregation, granule release and pro-coagulant function [3,4].…”

“…Up on platelet activation and adhesion, calcium elevation is associated with increased levels of intracellular ROS which oxidize cysteine residues located on cysteine-rich domain of ADAMs directly activating these proteolytic molecules to shed adhesion receptors. On the other hand, the interaction of ROS with intracellular cytoplasmic domains of ADAMs may also increase their a nity with substrate [1,18]. In addition, direct and indirect interactions of ROS with cytoplasmic domain of GPVI can also modulate its shedding events.…”