Class III PI3K Positively Regulates Platelet Activation and Thrombosis via PI(3)P-Directed Function of NADPH Oxidase

Abstract

Platelet VPS34 is critical for thrombosis but dispensable for hemostasis. VPS34 regulates platelet activation by influencing NOX assembly.

Response by Liu and Hu to Letter Regarding Article, “Class III PI3K Positively Regulates Platelet Activation and Thrombosis via PI(3)P-Directed Function of NADPH Oxidase”

“…With the importance of NOXs in platelet function emerging and their regulation mechanism unveiling, such as suggested by the study of Delaney et al 2 and ours, 1 we agree with the authors that it is imperative for future studies to further reveal the regulation network involving NOX isoforms and VPS34 in the context of platelet activation and thrombosis.…”

“…Nevertheless, both our study 1 and the study conducted by Delaney et al 2 demonstrate that low dose agonists (thrombin, 0.018 U/mL and 0.025 U/mL; collagen, 0.5 μg/mL; or CRP, 0.5 μg/mL) still activate significant ROS generation in platelets deficiency of NOX1, NOX2, or VPS34, suggesting the existence of other mechanisms of ROS generation independent of these proteins. The NOX family consists of 7 catalytic homologues, 7,8 in addition to NOX1 and NOX2, NOX4 is also detected in platelets.…”

“…1 Our conclusion that platelet VPS34 functions through NOX (likely the isoform NOX2) and the generation of ROS thereof is based on the observations as follows: (1) VPS34 deficiency impairs NOX2 assembly; (2) VPS34 deficiency reduces the production of ROS; (3) NOX inhibition by DPI (diphenyleneiodonium) abolishes the aggregation difference between VPS34 −/− and wild-type platelets, and supplementation of H 2 O 2 rescues the aggregation defect of VPS34 −/− platelets. Similar observation is obtained in human platelets by using VPS34 inhibitor 3-ma.…”

ROS Promote Ox-LDL-Induced Platelet Activation by Up-Regulating Autophagy Through the Inhibition of the PI3K/AKT/mTOR Pathway

“…Furthermore, a subsequent study confirmed that 3-MA suppresses autophagy by inhibiting class III PI3K [58]. The inhibitor of class III PI3K 3-MA blocks the plasma membrane translocation of important cytoplasmic subunits of NOX2 NADPH oxidase, further affecting the assembly and activation of NOX2 complex on the platelet membrane and subsequently reducing ROS production, ultimately affecting platelet activation and thrombosis [59]. Furthermore, the NOX2 NADPH was identified as one of the key sources of ROS, and a recent study has revealed a novel role for the NOX2 NADPH oxidase in the activation of autophagy [60].…”

Thrombotic Regulation From the Endothelial Cell Perspectives

“…This mechanism is in concert with the role of platelet ROS in thrombus formation: platelet-specific deficiency of class III phosphoinositide 3-kinase (also known as vacuolar protein sorting 34) attenuates thrombosis via influencing nicotinamide adenine dinuclectide phosphate oxidases assembly. 59 Given the complexity of ROS signals, how to therapeutically modulate the levels of endothelial ROS to curtail thrombosis warrants further study. Interestingly, in a randomized, placebo controlled clinical trial in patients with antiphospholipid syndrome, treatment with ubiquinol, the reduced equivalent of coenzyme Q10, improved endothelial function and reduced thrombotic risk markers, likely through reduced EC inflammation related to oxidative stress.…”