Activation of Platelet mTORC2/Akt Pathway by Anti-ß2GP1 Antibody Promotes Thrombosis in Antiphospholipid Syndrome.

BACKGROUND: Anti-ß2GP1 (ß2-glycoprotein 1) antibodies are the primary pathogenic antibody to promote thrombosis in antiphospholipid syndrome (APS), yet the underlying mechanism remains obscure. We aimed to explore the intracellular pathway that mediated platelet activation. METHODS: Platelets were isolated from patients with APS and subjected to RNA sequencing. Platelet aggregation, the release of platelet granules, platelet spreading, and clot retraction were detected to evaluate platelet activation. We purified anti-ß2GP1 antibodies from patients with APS and the total IgG from healthy donors to stimulate platelets with/without FcγRIIA (Fcγ receptor IIA) blocking antibody or Akt (protein kinase B) inhibitor. Platelet-specific Sin1 (stress-activated protein kinase-interacting protein) deficiency mice were established. The thrombus model of inferior vena cava flow restriction, ferric chloride-induced carotid injury model, and laser-induced vessel wall injury in cremaster arterioles model were constructed after administration of anti-ß2GP1 antibodies. RESULTS: Combined RNA sequencing and bioinformatics analysis suggested that APS platelets exhibited increased levels of mRNA associated with platelet activation, which was in line with the hyperactivation of APS platelets in response to stimuli. Platelet activation in APS platelets was accompanied by upregulation of the mTORC2 (mammalian target of the rapamycin complex 2)/Akt pathway and increased levels of SIN1 phosphorylation at threonine 86. Anti-ß2GP1 antibody derived from patients with APS enhanced platelet activation and upregulated the mTORC2/Akt pathway. Moreover, the Akt inhibitor weakened the potentiating effect of the anti-ß2GP1 antibody on platelet activation. Notably, Sin1 deficiency suppresses anti-ß2GP1 antibody-enhanced platelet activation in vitro and thrombosis in all 3 models. CONCLUSIONS: This study elucidated the novel mechanism involving the mTORC2/Akt pathway, which mediates the promotion of platelet activation and induction of thrombosis by the anti-ß2GP1 antibody. The findings suggest that SIN1 may be a promising therapeutic target for the treatment of APS.