Abstract WP351: Lung-Specific Extracellular Superoxide Dismutase Blocks Neutrophil-Mediated Toxicity in Brain Ischemia-Reperfusion

Abstract

Introduction: Tissue damage and neuroinflammatory responses associated with cerebral ischemia trigger a systemic immune response that exacerbates brain injury during reperfusion and adversely influences functional recovery. Polymorphonuclear neutrophils (PMNs) are the first-line response to inflammation following acute brain injury, and evidence implicates lung-dependent PMN depriming as a critical endogenous protective mechanism against reperfusion injury. Methods: We explored mechanisms of PMN priming and neurotoxicity with in vivo modeling of systemic inflammation after brain ischemia-reperfusion as well as cellular culture experiments. Using transgenic mice overexpressing the human antioxidant gene superoxide dismutase 3 in the lung (TgSOD3), we tested the hypothesis that manipulation of the lung’s redox environment could mitigate PMN activation and post-ischemic brain injury. Injury was induced by occlusion of the common carotid and basilar arteries followed by reperfusion and lipopolysaccharide-induced systemic inflammation. To assess cell interactions using live microscopy, we cultured primary cortical neurons after oxygen-glucose deprivation (OGD) with primed PMNs from wild-type or TgSOD3 mice. Results: Our results show that pulmonary SOD3 protects against peripheral PMN activation, lung injury, brain injury, and neuroinflammation after ischemia/reperfusion with systemic inflammation. We also found that PMNs from TgSOD3 mice are less toxic to post-OGD cultures compared to wild-type PMNs. Our data indicate that direct cell-cell contact is required for PMN-dependent neurotoxicity in mixed cellular cultures and that pre-exposure of neurons to OGD amplifies this response. Analyses reveal that PMNs effect a considerable degree of neuritic damage in vitro , while in vivo modeling demonstrates cortical injury, blood-brain barrier compromise, PMN activation, and lung injury after reperfusion. Conclusion: Collectively, these studies expand our understanding of PMN-dependent mechanisms in post-ischemic toxicity, both directly on neurons and via effects on CNS inflammation, and argue that the inflammatory milieu within the lung may modulate CNS reperfusion injury via manipulation of peripheral PMN priming.