Coenzyme Q10 Attenuates Platelet Integrin αIIbβ3 Outside-in Signaling through Targeting cAMP/PKA Pathway and Inhibits Atherosclerosis
Authors: Yang Yan , Xu Xiaohong Ruby , Ni Heyu , Ma Liping , Ling Wenhua , Ya Fuli 
Published: October 2019

Abstract
Introduction: Platelet integrin αIIbβ3 outside-in signaling is crucial for platelet adhesion and aggregation, and contributes to atherogenesis. Coenzyme Q10 (CoQ10) has been implicated as a protective factor against cardiovascular diseases (CVDs), particularly atherosclerosis. However, whether CoQ10 attenuates atherosclerosis through inhibiting platelet function and αIIbβ3 outside-in signaling is unknown. The aim of this study was to explore whether CoQ10 affects platelet function and αIIbβ3 outside-in signalling and thus inhibiting the progress of atherosclerosis in vivo and the underlying mechanisms in vitro.
Methods: In vitro study, The murine platelet rich plasma (PRP) from C57BL/6J wild-type (WT) mice or human PRP and gel-filtered platelets were incubated with different concentrations (1, 10 or 100 μM) of CoQ10 or the vehicle control for 50 min. Platelet aggregation, spreading on fibrinogen (Fg) and clot retraction were determined. In addition, the effects of CoQ10 on platelet integrin αIIbβ3 inside-out signalling (e.g., talin-1 and kindlin-3 binding to integrin β3) were determined by immunoprecipitation, and outside-in signalling (e.g., phosphorylation of sarcoma tyrosine-protein kinase (c-Src), focal adhesion kinase (FAK), and β3 cytoplasmic tail, myosin light chain (MLC)) were determined by Western blotting. The levels of platelet ATP and cAMP were measured by ELISA assays. In vivo study, male homozygous apolipoprotein E-deficient (apoE-/-) mice (C57BL/6 genetic background) were fed either a standard normal AIN-93G diet (NC group), a Western-type diet (HFD group) or a Western-type diet supplemented with CoQ10 (1800 mg/kg diet) (CoQ10 group) for 12 weeks. Platelet aggregation, granule secretion, platelet spreading, clot retraction, integrin αIIbβ3 outside-in signalling, platelet-leukocyte interactions and carotid artery plaque area were also examined. In our randomized, double-blind, placebo-controlled trial, 101 hypercholesterolemic subjects were randomly administrated to 120 mg CoQ10 or placebo daily for 24 weeks. Platelet intracellular CoQ10 levels, platelet aggregation in PRP, platelet platelet factor 4 (PF-4) and C-C motif ligand 5 (CCL5) release, and platelet integrin αIIbβ3 outside-in signalling were also evaluated before and after 24 weeks of intervention.
Results: We found that CoQ10 inhibited human and WT mouse platelet aggregation, platelet spreading, granule secretion, and clot retraction in vitro and apoE-/- mice on a high fat diet. CoQ10 also reduced atherosclerosis and platelet-monocyte aggregation in apoE-/- mice. The inhibitory effects of CoQ10 is mediated by attenuated αIIbβ3 outside-in signalling pathway (e.g., attenuation of phosphorylation of c-Src, FAK, and β3 cytoplasmic tail, and MLC in thrombin-activated platelets or platelets exposed to immobilized Fg), which requires up-regulation of the cAMP/PKA pathway, where CoQ10 inhibited phosphodiesterase 3A activity and activated the A2A adenosine receptor. However, CoQ10 did not affect platelet integrin αIIbβ3 inside-out signalling pathway, platelet cellular ATP, or platelet apoptosis (the mitochondrial membrane potential and phosphatidylserine exposure). Moreover, our clinical trial in dyslipidemic patients demonstrated that CoQ10 supplementation attenuated platelet aggregation, which was positively correlated with the increased platelet CoQ10 concentrations, inhibited αIIbβ3 outside-in signalling and decreased platelet PF-4 and CCL5 secretion.
Conclusions: We present new data to suggest that CoQ10 plays a novel role in attenuating platelet function and integrin αIIbβ3 outside-in signalling though targeting cAMP/PKA signalling cascade and thus inhibiting the progress of atherosclerosis. CoQ10 is therefore a promising agent for the prevention and/or treatment for cardiovascular disease.

Disclosures
No relevant conflicts of interest to declare.