Targeting Myeloid-Specific Integrin alpha9beta1 Improves Short and Long-Term Stroke Outcomes in Murine Models With Preexisting Comorbidities by Limiting Thrombosis And Inflammation.

Rationale: 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 alpha9beta1 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 sought to determine the mechanistic role of myeloid-specific alpha9beta1 in the progression of ischemic stroke in murine models with preexisting comorbidities. Methods and Results: We generated novel myeloid-specific alpha9-deficient (alpha9(-/-)) wild-type (alpha9(fl/fl)LysMCre(+/-)), hyperlipidemic (alpha(fl/fl)LysMCre(+/-)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 two models of experimental stroke: filament and embolic. We found that peripheral neutrophils displayed elevated alpha9 expression following stroke. Irrespective of sex, genetic deletion of alpha9 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 alpha9(-/-) mice was due to marked decrease in cerebral thrombo-inflammatory response as evidenced by reduced fibrin, platelet thrombi, neutrophil, NETosis and decreased phospho-NF-kappaB, TNFalpha, and IL-1beta levels. alpha9(-/-) mice were less susceptible to FeCl3 injury-induced carotid artery thrombosis that was concomitant with improved regional CBF following stroke as revealed by laser speckle imaging. Mechanistically, fibronectin containing extra domain A, a ligand for integrin alpha9, partially contributed to alpha9-mediated stroke exacerbation. Infusion of a specific anti-integrin alpha9 inhibitor into hyperlipidemic mice following reperfusion significantly reduced infarct volume and improved short and long-term functional outcomes up to 28 days. Conclusions: We provide genetic and pharmacologic evidence for the first time that targeting myeloid-specific integrin alpha9beta1 improves short and long-term functional outcome in stroke models with preexisting comorbidities by limiting cerebral thrombosis and inflammation.