Potential roles of neutrophils and platelets in the pathophysiology of intracranial aneurysms have been long
suggested by clinical observations. However, the exact mechanism by which neutrophils and platelets work to
promote the rupture of intracranial aneurysms is not well understood. Activated neutrophils can release
decondensed DNA decorated with neutrophil enzymes such as neutrophil elastase and myeloperoxidase,
resulting in the formation of Neutrophil Extracellular Traps (NETs) and the death of neutrophils (NETosis).
NETs were originally described as a structure that can trap and dissolve pathogens. However, recent studies
suggest roles of NETs in sterile diseases that involve vascular inflammation including atherosclerosis,
vasculitis, and venous thrombosis. Interactions between NETs and platelets may result in a vicious cycle of
NET formation and platelet activation that leads to the excessive vascular wall damages and aneurysmal
rupture. Our preliminary studies show that NETs exist in both human intracranial aneurysms and experimental
mouse aneurysms. In addition, mice lacking protein arginine deiminases-4 (PAD4), an enzyme required for the
NET formation, had a reduced rupture rate.
We hypothesize that NETs, neutrophil extracellular traps, can promote the development of intracranial
aneurysm rupture through the vicious cycle of neutrophil and platelet activation. In Aim 1, we will test neutrophil
PAD4-deficient mice have a lower rupture rate and reduce NET formations compared to the control mice. In
Aim 2, we will test whether the pharmacological prevention of NET formation by PAD4 inhibitors (Cl-amidine
and GSK484) or the resolution of NETs by deoxyribonuclease reduces aneurysmal rupture. In Aim 3, we will
test whether platelets and neutrophil-platelet interactions contribute to aneurysmal rupture. We will test
whether thrombocytopenic mice have reduced NET formations and lower rupture rates. We will also study the
contribution of P-selectin or CD11b/CD18-mediated neutrophil-platelet interactions to the development of
The proposed studies will provide new insights into the roles of NETs and their interactions with platelets in the
development of aneurysmal rupture. The results will be a basis for future studies to develop new therapies that
target NETs and platelet-neutrophil interactions for the prevention of aneurysmal rupture.