Reactive Oxygen Species activate the NLRP3 Inflammasome in a model of lung transplant

Abstract

BackgroundLung transplant involves a period of storage (ischemia) followed by the transplant (reattachment or reperfusion) event. The resultant ischemia‐reperfusion (I/R) injury, clinically known as primary graft dysfunction (PGD), is the most common cause for post‐transplant failure. Indeed, studies have shown that the poor outcome of lung transplant is primarily due to PGD that drives morbidity and mortality in ~30% of lung transplant recipients. We showed earlier, that one of the pivotal events with lung I/R associated with transplant is the production of reactive oxygen species (ROS). We also showed that this ROS generation is not the result of hypoxia‐deoxygenation as the lung oxygen supply is not compromised with stop or restart of blood flow. ROS produced with lung I/R reflects “flow” sensitive endothelial signaling that triggers NADPH oxidase‐2 (NOX2) activation. We postulated that injury with transplant was caused due to ROS initiated inflammation signaling. Among the inflammatory moieties of interest to us was the NOD like receptor protein 3 (NLRP3 inflammasome), which has been reported to be a major cause of cell death with I/R in systemic organs via pathways that were anoxia/hypoxia dependent. Could NLRP3 be activated by normoxic lung I/R as well? To answer this, we investigated NLRP3 activation and the mechanism of its regulation with lung I/R. Our hypothesis was that NOX2 activated with I/R regulates the NLRP3 inflammasome which in turn is a major driver of graft injury (PGD).MethodsMice (wild type and NOX2 null) were subjected lung I/R by hilar clamp and NLRP3 inflammasome activation measured by monitoring the colocalization of NLRP3 with its adaptor molecule ASC. Lung Injury was monitored by indices such as lipid peroxidation, isoprostanes and lung wet to dry ratio. The correlation between NLRP3 and PGD in post‐transplant human subjects was assessed by monitoring plasma NLRP3 and PGD outcome (obtained from Lung Transplant Outcomes Group Database).ResultsWe observed a ROS dependent increase in NLRP3 activation post lung I/R. We also found that NLRP3 blockade significantly reduced lung injury. Additionally, post‐transplant (human) recipients with detectable NLRP3 protein in plasma developed PGD.ConclusionThe NLRP3 inflammasome is regulated via NOX2 induced ROS production and plays a crucial role in injury with I/R. It can thus be considered as a risk factor with PGD.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.