Migfilin supports hemostasis and thrombosis through regulating platelet aIIbβ3 outside-in signaling

Elucidating the regulation mechanism of integrin aIIbβ3 is key to understanding platelet biology and thrombotic diseases. Previous in vitro studies have implicated a role of migfilin in the support of platelet aIIbβ3 activation, however, contribution of migfilin to thrombosis and hemostasis in vivo and a detailed mechanism of migfilin in platelets are not known. In this study, through migfilin knock-out (migfilin(-/-)) mice, we report that migfilin is a pivotal positive regulator of hemostasis and thrombosis. Migfilin(-/-) mice show a nearly doubled tail-bleeding time and a prolonged occlusion time in FeCl(3)-induced mesenteric arteriolar thrombosis. Migfilin deficiency impedes platelet thrombi formation on a collagen surface and impairs platelet aggregation and dense-granule secretion. Supported by characteristic functional readings and the phosphorylation status of distinctive signaling molecules in the bidirectional signaling processes of aIIbβ3, the functional defects of migfilin(-/-) platelets appear to be mechanistically associated with a compromised outside-in signaling, rather than inside-out signaling. A synthesized cell-permeable migfilin peptide harboring filamin A binding sequence rescued the defective function and phosphorylation of signaling molecules of migfilin(-/-) platelets. Finally, migfilin does not influence the binding of filamin A and β3 subunit of aIIbβ3 in resting platelets, but hampers the re-association of filamin A and β3 during the conduct of outside- in signaling, suggesting that migfilin functions through regulating the interaction dynamics of aIIbβ3 and filamin A in platelets. Our study enhances the current understanding of platelet integrin aIIbβ3-mediated outside-in signaling and proves that migfilin is an important regulator for platelet activation, hemostasis and thrombosis.