Currently, there is no effective intervention available that can reduce brain damage following reperfusion. Clinical studies suggest a positive correlation between the increased influx of neutrophils and severity of
brain injury following reperfusion.
Integrin α9β1 is highly expressed on activated neutrophils and contributes to stable adhesion, but its role in
stroke outcome has not been demonstrated to date.
OBJECTIVE: We generated novel myeloid-specific α9-deficient (α9-/-) wild type (α9fl/flLysMCre+/-), hyperlipidemic (α9fl/flLysMCre+/-
Apoe-/-), and aged (bone marrow chimeric) mice to evaluate
stroke outcome. Susceptibility to
ischemia/reperfusion injury was evaluated at 1, 7, and 28 days following reperfusion in 2 models of experimental
stroke: filament and embolic. We found that peripheral neutrophils displayed elevated α9 expression following
stroke. Irrespective of sex, genetic deletion of α9 in myeloid cells improved short- and long-term
stroke outcomes in the wild type, hyperlipidemic, and aged mice. Improved
stroke outcome and enhanced survival in myeloid-specific α9-/- mice was because of marked decrease in cerebral thromboinflammatory response as evidenced by reduced
fibrin, platelet thrombi, neutrophil, NETosis, and decreased phospho-NF-κB (nuclear factor-κB), TNF (
tumor necrosis factor)-α, and IL (interleukin)-1β levels. α9-/- mice were less susceptible to FeCl3 injury-induced
carotid artery thrombosis that was concomitant with improved regional cerebral blood flow following
stroke as revealed by
laser speckle imaging. Mechanistically,
fibronectin containing extra domain A, a
ligand for
integrin α9, partially contributed to α9-mediated
stroke exacerbation. Infusion of a specific anti-
integrin α9 inhibitor into hyperlipidemic mice following reperfusion significantly reduced
infarct volume and improved short- and long-term functional outcomes up to 28 days.
CONCLUSIONS: