The Mechanism Of Platelet Sin1 In Regulation Of Ischaemia-induced Microthrombosis

Introduction—Microthrombosis as a serious consequence of myocardial infarction,impairs the microvascular environment and increases the occurrences of heart failure,arrhythmia and death.Abnormal platelet activation is the suspected cause of microthrombus formation,yet the mechanism and effect of platelet activation on ischaemic microthrombosis are poorly defined.Mammalian target of rapamycin(m TOR)is required for cell proliferation and metabolism in response to nutrients,stress and reactive oxygen species(ROS)and activates a group of AGC kinases that includes Akt,serum/glucocorticoid induced kinase(SGK),and protein kinase C(PKC).We present evidence that Sin1,an essential component of the m TOR complex 2(m TORC2),positively regulates platelet activation via integrin-mediated signalling and hypoxia responses in platelets in ischaemia-induced microthrombosis.Methods and results—Here,we found that the phosphorylation of the m TORC2 target Akt at S473 was significantly elevated in platelets from the distal end of LAD obstructions from patients who underwent off-pump coronary artery bypass grafting(OPCABG)compared to platelets from healthy subjects.Consistent with this finding,phosphorylation of T86 in Sin1 was also dramatically increased.Importantly,the augmented levels of phosphorylated Sin1 and Akt in platelets from 61 preoperative patients with ST segment myocardial infarction(MI)correlated well with the no-reflow phenomena observed following revascularization(relative phospho-Akt S473 level: odds ratio was 3.62,95% CI was 1.75-7.48,P<0.01;relative phospho-Sin1 T86 level: odds ratio was 2.12,95% CI was 1.30-3.46,P<0.01).Platelet-specific Sin1-deficiency mice and Sin1 T86 phosphorylation deficiency mice were established to explore the underlying mechanisms in platelet activation.Mechanistically,Sin1 T86 phosphorylation amplifies m TORC2-mediated downstream signals;it is also required for integrin outside-in signaling and plays a role in generating hypoxia/ROS through a mechanism that is partially mediated by the suppression of SOD2 and SIRT3 expression.Importantly,Sin1 deletion in platelets protected mice from ischaemia-induced microvascular embolization and subsequent heart dysfunction in a mouse model of MI.Conclusions—Together,the results of our study reveal a novel role for Sin1 in platelet activation.Thus,Sin1 may be a valuable therapeutic target for interventions for ischaemia-induced MI deterioration.