DNAse-dependent, NET-independent pathway of thrombus formation in vivo

The contribution of NETs (neutrophil extracellular traps) to thrombus formation has been intensively documented in both arterial and venous thrombosis in mice. We previously demonstrated that adenosine triphosphate (ATP)-activated neutrophils play a key role in initiating the tissue factor-dependent activation of the coagulation cascade, leading to thrombus formation following laser-induced injury. Here, we investigated the contribution of NETs to thrombus formation in a laser-induced injury model. In vivo, treatment of mice with DNase-I significantly inhibited the accumulation of polymorphonuclear neutrophils at the site of injury, neutrophil elastase secretion, and platelet thrombus formation within seconds following injury. Surprisingly, electron microscopy of the thrombus revealed that neutrophils present at the site of laser-induced injury did not form NETs. In vitro, ATP, the main neutrophil agonist present at the site of laser-induced injury, induced the overexpression of PAD4 and CitH3 but not NETosis. However, compared to no treatment, the addition of DNase-I was sufficient to cleave ATP and adenosine diphosphate (ADP) in adenosine. Human and mouse platelet aggregation by ADP and neutrophil activation by ATP were also significantly reduced in the presence of DNase-I. We conclude that following laser-induced injury, neutrophils but not NETs are involved in thrombus formation. Treatment with DNase-I induces the hydrolysis of ATP and ADP, leading to the generation of adenosine and the inhibition of thrombus formation in vivo.