NLRP3 Knockout Protects against Lung Injury Induced by Cerebral Ischemia–Reperfusion

Abstract

Background and Purpose. Stroke-associated pneumonia (SAP) is a common complication after stroke that increases the mortality of patients. Although there have been many studies suggesting that stroke can increase patient susceptibility to pneumonia, it is still unknown whether the treatment of stroke can also improve lung injury. We used NLRP3-knockout (NLRP3-KO) mice to verify that an improvement in brain injury would also be beneficial to lung injury and further confirm the relationship between stroke and pneumonia. Methods. C57/BL6 wild-type (WT) and NLRP3-KO mice were used to construct middle cerebral artery occlusion (MCAO) models. 2,3,5-Triphenyltetrazolium chloride (TTC) was used to evaluate brain damage, and neurological deficits were assessed. Then, lung tissue injury was examined in the different groups of mice by hematoxylin-eosin (HE) staining. Inflammation (macrophage and neutrophil infiltration, NLRP3-associated inflammatory molecules) and oxidative stress (reactive oxygen species, ROS) in the lungs were comprehensively examined by immunofluorescence staining and Western blotting. Results. First, our findings demonstrated that NLRP3 knockout had a protective effect against cerebral ischemia–reperfusion injury after MCAO. Second, by reducing brain damage after MCAO, lung inflammation was also alleviated. Immunofluorescence staining showed that NLRP3-KO-MCAO mice had reduced inflammatory effector molecule (caspase-1 and IL-1β) expression and macrophage and neutrophil infiltration in the lung, as well as remissive oxidative stress state in the lung, compared with WT-MCAO mice. We also observed a decrease in phosphorylated p65 (p-p65) (an NF-κB factor) in NLRP3-KO-MCAO mice, suggesting that the NF-κB pathway was involved in the protective effect of NLRP3 gene knockout on stroke-induced lung injury. Conclusions. NLRP3 inflammasome knockout not only is beneficial for cerebral ischemia–reperfusion injury but also reduces the severity of poststroke lung injury by reducing brain damage. It has been confirmed that there is a relationship between central insult and peripheral organ injury, and protecting the brain can prevent peripheral organ damage.