Abstract
Objective: Recent studies indicate that the innate immune system is not only activated by exogenous pathogens and pollutants, but also by endogenous danger signals released during ischemia and necrosis. As activation triggers (cellular K+ extrusion, ROS production) for the innate immune NALP3 inflammasome protein complex overlap with those for cardiac ischemia-reperfusion (I/R) and ischemic preconditioning (IPC), we explored the possibility that the NALP3 inflammasome is involved in IPC and acute I/R injury of the heart. Methods & Results: Baseline performance and I/R injury was investigated in isolated, Langendorff-perfused hearts from wild-type, ASC-/- and NALP3-/- mice. Baseline cardiac performance was unaffected by genetic deletion of NALP3 inflammasome components. Deletion of the ASC and NALP3 component exacerbated IR injury on mechanical parameters of the heart. However, deficiency in ASC or NALP3 was without effect on cell death (LDH release during reperfusion). In a separate series we subjected these same hearts to IPC, consisting of 3 x 5 min I/R preceding the 35 min I. IPC protected WT and ASC-/- hearts against IR injury (improved function and less cell death). However, no IPC effects on function or cell death were observed in NALP3-/- hearts. NALP3-/- hearts had significantly decreased cardiac IL-6 levels with a trend towards lower Il-1β levels at end reperfusion, suggesting abrogating of IPC through diminished IL-6 and/or Il-1β signalling. However, subsequent experiments showed that inhibition of the IL-1r receptor with the IL-1 receptor inhibitor Anakinra (100 mg/L) was without effect on IPC in WT hearts. In contrast, neutralising IL-6 using an antibody against IL-6 in WT hearts abrogated IPC in NALP3-/- hearts. Conclusions: The data suggest that the innate immune NALP3 protein, in an NALP3-inflammasome-independent fashion, is an integral component of IPC in the isolated heart, possibly through an IL-6 dependent mechanism
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