Phosphatidylinositol 3-kinase (PI3K) isoforms PI3K␤ and PI3K␥ are implicated in platelet adhesion, activation, and aggregation, but their relative contribution is still unclear or controversial. Here, we report the first comparative functional analysis of platelets from mice expressing a catalytically inactive form of PI3K␤ or PI3K␥. We demonstrate that both isoforms were similarly required for maximal activation of the small GTPase Rap1b and for complete platelet aggregation upon stimulation of G protein-coupled receptors for adenosine 5-diphosphate (ADP) or U46619. Their contribution to these events, however, was largely redundant and dispensable. However, PI3K␤, but not PI3K␥, enzymatic activity was absolutely required for Akt phosphorylation, Rap1 activation, and platelet aggregation downstream of the immunoreceptor tyrosinebased activation motif (ITAM)-bearing receptor glycoprotein VI (GPVI). Moreover, PI3K␤ was a major essential regulator of platelet adhesion to fibrinogen and of integrin ␣ IIb ␤ 3 -mediated spreading. These results provide genetic evidence for a crucial and selective role of PI3K␤ in signaling through GPVI and integrin ␣ IIb IntroductionThe phosphatidylinositol 3-kinase (PI3K) is implicated in platelet activation downstream of G protein-coupled receptors (GPCRs), immunoreceptor tyrosine-based activation motif (ITAM)-bearing receptors, as well as integrins. 1 The different PI3K isoforms are grouped in 3 classes, I, II, and III. Class I PI3K includes the p85-associated members PI3K␣, PI3K␤, and PI3K␦ (class IA), as well as the PI3K␥ isoform (class IB). Although all class I members are expressed in platelets, PI3K␥ and PI3K␤ are considered to play a major role in platelet physiology, 1,2 but their relative contribution is still controversial.PI3K␥ is activated by G protein ␤␥ dimers, and, in platelets, it has been implicated in Rap1b activation and integrin ␣ IIb ␤ 3 -supported aggregation downstream of the G i -coupled P2Y12 adenosine 5Ј-diphosphate (ADP) receptor. 3,4 This model has however been challenged by other studies, proposing a predominant role of PI3K␤ rather than PI3K␥ in ADP-induced platelet activation. 5,6 In addition, the finding that PI3K␥ also functions as a scaffold protein 7 supported a model for a kinaseindependent contribution of PI3K␥ in ADP-mediated platelet activation. 8 In platelets, PI3K is also activated upon stimulation of the ITAM-bearing collagen receptor glycoprotein VI (GPVI)/FcR ␥-chain. 9 Although there is evidence that a class IA member is involved, 10 its identity is still unknown. Similarly, integrin ␣ IIb ␤ 3 recruitment activates PI3Ks. The involvement of a class II member has been hypothesized, 11 but a possible role for class I isoforms clearly emerges from a more recent study. 12 The specific contribution of PI3K␥ and PI3K␤ in platelet activation has remained largely elusive, mainly because of the early embryonic lethality caused by genetic ablation of PI3K␤ in mice, 13 and because the interpretation of the analysis of PI3K␥ knockout mice turned out...

No abstract

Extracellular vesicles (EVs) are well-established mediators of cell-to-cell communication. EVs can be released by every cell type and they can be classified into three major groups according to their biogenesis, dimension, density, and predominant protein markers: exosomes, microvesicles, and apoptotic bodies. During their formation, EVs associate with specific cargo from their parental cell that can include RNAs, free fatty acids, surface receptors, and proteins. The biological function of EVs is to maintain cellular and tissue homeostasis by transferring critical biological cargos to distal or neighboring recipient cells. On the other hand, their role in intercellular communication may also contribute to the pathogenesis of several diseases, including thrombosis. More recently, their physiological and biochemical properties have suggested their use as a therapeutic tool in tissue regeneration as well as a novel option for drug delivery. In this review, we will summarize the impact of EVs released from blood and vascular cells in arterial and venous thrombosis, describing the mechanisms by which EVs affect thrombosis and their potential clinical applications.

No abstract