Targeting Myeloid-Cell Specific Integrin α9β1 Inhibits Arterial Thrombosis in Mice

Evidence suggests that neutrophils contribute to thrombosis via several mechanisms, including neutrophil extracellular traps (NETs) formation. Integrin alpha9beta1 is highly expressed on neutrophils when compared with monocytes. It undergoes affinity upregulation on neutrophil activation, and stabilizes adhesion to the activated endothelium. The role of integrin alpha9 in arterial thrombosis remains unexplored. We generated novel myeloid cell-specific integrin alpha9-/- mice (alpha9fl/flLysMCre+) to study the role of integrin alpha9 in arterial thrombosis. alpha9fl/fl littermates were used as controls. We report that alpha9fl/flLysMCre+ mice were less susceptible to arterial thrombosis in ferric chloride (FeCl3) and laser injury-induced thrombosis models with unaltered hemostasis. Neutrophil elastase-positive cells were significantly reduced in alpha9fl/flLysMCre+ mice concomitant with reduction in neutrophil count, myeloperoxidase levels, and red blood cells in the FeCl3 injury-induced carotid thrombus. The percentage of cells releasing NETs was significantly reduced in alpha9fl/flLysMCre+ mouse neutrophils stimulated with thrombin-activated platelets. Furthermore, we found a significant decrease in neutrophil-mediated platelet aggregation and cathepsin-G secretion in alpha9fl/flLysMCre+ mice. Transfusion of alpha9fl/fl neutrophils in alpha9fl/flLysMCre+ mice restored thrombosis similar to alpha9fl/fl mice. Treatment of wild-type mice with anti-integrin alpha9 antibody inhibited arterial thrombosis. This study identifies the potential role of integrin alpha9 in modulating arterial thrombosis.