Phosphoinositide 3-kinase p110α negatively regulates thrombopoietin-mediated platelet activation and thrombus formation

Abstract

Phosphoinositide 3-kinase (PI3K) plays an important role in platelet function and contributes to platelet hyperreactivity induced by elevated levels of circulating peptide hormones, including thrombopoietin (TPO). Previous work established an important role for the PI3K isoform; p110β in platelet function, however the role of p110α is still largely unexplored. Here we sought to investigate the role of p110α in TPO-mediated hyperactivity by using a conditional p110α knockout (KO) murine model in conjunction with platelet functional assays. We found that TPO-mediated enhancement of collagen-related peptide (CRP-XL)-induced platelet aggregation and adenosine triphosphate (ATP) secretion were significantly increased in p110α KO platelets. Furthermore, TPO-mediated enhancement of thrombus formation by p110α KO platelets was elevated over wild-type (WT) platelets, suggesting that p110α negatively regulates TPO-mediated priming of platelet function. The enhancements were not due to increased flow through the PI3K pathway as phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P) formation and phosphorylation of Akt and glycogen synthase kinase 3 (GSK3) were comparable between WT and p110α KO platelets. In contrast, extracellular responsive kinase (ERK) phosphorylation and thromboxane (TxA) formation were significantly enhanced in p110α KO platelets, both of which were blocked by the MEK inhibitor PD184352, whereas the p38 MAPK inhibitor VX-702 and p110α inhibitor PIK-75 had no effect. Acetylsalicylic acid (ASA) blocked the enhancement of thrombus formation by TPO in both WT and p110α KO mice. Together, these results demonstrate that p110α negatively regulates TPO-mediated enhancement of platelet function by restricting ERK phosphorylation and TxA synthesis in a manner independent of its kinase activity.

The probable role and therapeutic potential of the PI3K/AKT signaling pathway in SARS-CoV-2 induced coagulopathy

“…In addition, it has been reported that pharmacologic inhibition of PI3Kα contributes to suppression of insulin-like growth factor-1 (IGF-1) induced AKT activation, inhibition of platelet activation and thrombus formation in cultured human platelets [ 37 ]. In a closer inspection, another study showed that PI3Kα inhibition augments thrombopoietin-mediated platelet activation and thrombus formation through restricting thromboxane A2 synthesis and extracellular signal-regulated kinase (ERK) phosphorylation [ 38 ]. Additionally, loureirin, a flavonoid extracted from dragon’s blood (a deep red resin secreted from Dracaena ), has been shown to suppress platelet activation through PI3K/AKT signaling pathway inhibition [ 39 ].…”

Opposing Roles of GSK3α and GSK3β Phosphorylation in Platelet Function and Thrombosis

“…TxA 2 generation was assessed by measuring TxB 2 in platelet supernatants using a commercially available colorimetric ELISA kit (Enzo Life Sciences, Exeter, UK) as previously described [ 49 ].…”

Increased Platelet Activation demonstrated by Elevated CD36 and P-Selectin Expression in 1-Year Post-Recovered COVID-19 Patients

“…7,8 The phenomenon of COVID-19 platelet activation is likely due to the association between inflammation/infection and platelet production. Platelet production and activation is driven by thrombopoietin, 9,10 which is upregulated by inflammatory cytokines activated in COVID-19 infection, such as interleukin-6. Platelets also possess cell surface receptors that contribute to immune cell interaction and function.…”