Targeting Myeloid-Specific Integrin Alpha 9 Beta 1 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 alpha 9 beta 1 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 alpha 9 beta 1 in the progression of ischemic stroke in murine models with preexisting comorbidities. Methods and Results: We generated novel myeloid-specific alpha 9-deficient (alpha 9(-/-)) wild type (alpha 9(fl/fl)LysMCre(+/-)), hyperlipidemic (alpha 9(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 2 models of experimental stroke: filament and embolic. We found that peripheral neutrophils displayed elevated alpha 9 expression following stroke. Irrespective of sex, genetic deletion of alpha 9 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 alpha 9(-/-)mice was because of marked decrease in cerebral thromboinflammatory response as evidenced by reduced fibrin, platelet thrombi, neutrophil, NETosis, and decreased phospho-NF-kappa B (nuclear factor-kappa B), TNF (tumor necrosis factor)-alpha, and IL (interleukin)-1 beta levels.alpha 9(-/-)mice were less susceptible to FeCl(3)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 alpha 9, partially contributed to alpha 9-mediated stroke exacerbation. Infusion of a specific anti-integrin alpha 9 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 pharmacological evidence for the first time that targeting myeloid-specific integrin alpha 9 beta 1 improves short- and long-term functional outcomes in stroke models with preexisting comorbidities by limiting cerebral thrombosis and inflammation.