The class II PI 3-kinase, PI3KC2α, links platelet internal membrane structure to shear-dependent adhesive function

Abstract

PI3KC2a is a broadly expressed lipid kinase with critical functions during embryonic development but poorly defined roles in adult physiology. Here we utilize multiple mouse genetic models to uncover a role for PI3KC2a in regulating the internal membrane reserve structure of megakaryocytes (demarcation membrane system) and platelets (open canalicular system) that results in dysregulated platelet adhesion under haemodynamic shear stress. Structural alterations in the platelet internal membrane lead to enhanced membrane tether formation that is associated with accelerated, yet highly unstable, thrombus formation in vitro and in vivo. Notably, agonist-induced 3-phosphorylated phosphoinositide production and cellular activation are normal in PI3KC2a-deficient platelets. These findings demonstrate an important role for PI3KC2a in regulating shear-dependent platelet adhesion via regulation of membrane structure, rather than acute signalling. These studies provide a link between the open canalicular system and platelet adhesive function that has relevance to the primary haemostatic and prothrombotic function of platelets.

Essential role of class II PI3K-C2α in platelet membrane morphology

“…Although these structural defects have a minor effect on primary hemostasis, they are associated with a marked alteration in the function of platelets in arterial thrombosis. Interestingly, a very recent study by Mountford et al, 39 using knock-down mice models of PI3K-C2a, also highlights the key role of PI3K-C2a in the regulation of membrane structure and dynamics in platelets. In addition to similarities in the phenotypes of our KI and their knock-down models, several differences exist, including a-granule defects and thrombus stability, that may come from the putative scaffolding role of PI3K-C2a.…”

PI3K/Akt in platelet integrin signaling and implications in thrombosis

“…Deletion of PI3KC2a in platelets causes dysregulation of platelet adhesion under flow and promotes the more rapid formation of larger, but highly unstable platelet thrombi (Mountford et al, 2015). Interestingly, PI3KC2a was found to play no role in platelet activation, integrin signaling and 3-phosphoinositides generation in platelets, but its deficiency was markedly associated to a significant alteration of the open canalicular system, the major intraplatelet membrane reservoir.…”

“…All class I PI3Ks isoforms are expressed in blood platelets together with two of the three class II PI3K isoforms, PI3KC2a and PI3KC2b (Mountford et al, 2015). Whereas very little information is available on the role of class II and III PI3Ks in platelet activation, the implication of class I enzymes has been deeply investigated mainly using pharmacological pan-inhibitors including first generation compounds wortmannin and LY294002, as well as more recently described drugs, such as S14161 (Eisenreich and Rauch, 2011;Yi et al, 2014).…”

Development of a novel strategy to target CD39 antithrombotic activity to the endothelial-platelet microenvironment in kidney ischemia–reperfusion injury

“…Assessment of tail bleeding times after rsol.CD39-PSGL-1 administration Mice were injected with saline or varying doses of rsol.CD39-PSGL-1 via the tail vein or orally administered clopidogrel (30 mg/kg; Plavix, Sanofi Winthrop, Paris, France) 2 h before, and tail transection bleed times and template tail bleed times were determined as described [20]. For template tail bleed times, mice were anaesthetized and a lateral incision 5 mm long and 2 mm deep, 1 cm from the tip of the mouse's tail was made using a scalpel blade.…”

“…The following semi-quantitative scale was used to evaluate the degree of tubular necrosis: 0, normal kidney; 1, minimal necrosis (<10% involvement); 2, mild necrosis (10-<25% involvement); 3, moderate necrosis (25-75% involvement); and 4, severe necrosis (>75% involvement) [20].…”