Apoptosis signal-regulating kinase 1 regulates immune-mediated thrombocytopenia, thrombosis, and systemic shock

Background: Immune complexes (ICs) bind to and activate platelets via Fc gamma RIIA, causing patients to experience thrombocytopenia, as well as an increased risk of forming occlusive thrombi. Although platelets have been shown to mediate IC-induced pathologies, the mechanisms involved have yet to be fully elucidated. We identified that apoptosis signal-regulating kinase 1 (ASK1) is present in both human and mouse platelets and potentiates many platelet functions. Objectives: Here we set out to study ASK1's role in regulating IC-mediated platelet functions in vitro and IC-induced pathologies using an in vivo mouse model. Methods: Using human platelets treated with an ASK1-specific inhibitor and platelets fromFCGR2A/Ask1(-/-) transgenic mice, we examined various platelet functions induced by model ICs in vitro and in vivo. Results: We found that ASK1 was activated in human platelets following cross-linking of Fc gamma RIIA using either anti-hCD9 or IV.3 + goat-anti-mouse. Although genetic deletion or inhibition of ASK1 significantly attenuated anti-CD9-induced platelet aggregation, activation of the canonical Fc gamma RIIA signaling targets Syk and PLC gamma 2 was unaffected. We further found that anti-mCD9-induced cPla(2) phosphorylation and TxA(2) generation is delayed in Ask1 null transgenic mouse platelets leading to diminished delta-granule secretion. In vivo, absence of Ask1 protected FCGR2Atransgenic mice from thrombocytopenia, thrombosis, and systemic shock following injection of anti-mCD9. In whole blood microfluidics, platelet adhesion and thrombus formation on fibrinogen was enhanced by Ask1. Conclusions: These findings suggest that ASK1 inhibition may be a potential target for the treatment of IC-induced shock and other immune-mediated thrombotic disorders.