Abstract 5558: Inflammasome Activation in Cardiac Fibroblasts is Essential for Myocardial Ischemia-reperfusion Injury
Background: Inflammatory responses play a key role in the pathophysiology of myocardial ischemia-reperfusion (I/R) injury. We previously investigated the role of ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain), an adaptor protein that forms inflammasome whose activation leads to caspase-1-dependent interleukin (IL)-1β maturation, in myocardial I/R injury and found that ASC deficiency prevented IL-1β secretion and inflammatory cell infiltration, resulting in improving myocardial injury and remodeling. In this study, we investigated the mechanisms by which I/R initiates activation of inflammasome in the heart.
Methods and Results: To examine what kind of cells are responsible for inflammasome activation in the heart, primary cardiomyocytes (CM) and cardiac fibroblasts (CF) from the wild-type mice were prepared. Although ASC was clearly expressed in both CM and CF, IL-1β secretion was detected in only CF after stimulation with relatively high dose of lypopolysaccharide (LPS: 100 ng/mL). The intracellular pro-IL-1β accumulation in CF was similar between wild-type (WT) and ASC deficient (ASC−/−) mice; however, IL-1β processing and secretion were significantly inhibited in ASC−/−-CF, compared with that in WT-CF (p<0.01). Hypoxia/reoxygenation (H/R: 6 h of H following 18 h R) dramatically induced IL-1β secretion in CF after low dose (10 ng/mL) LPS priming. To determine the mechanisms by H/R might activate inflammasome, CF were treated with ATP (10 mM), HMGB1 (10 mg/mL), and K+ ionophore nigericin (1mM) after LPS priming. Marked IL-1β secretion was detected only in nigericin-treated CF. Further, H/R-induced IL-1β secretion was significantly inhibited by the treatment with antioxidant N-acetyl-L-cysteine (NAC: 10 mM), K+ channel blockers (glimepiride 10 mM, glibenclamide 10 mM, TEA 10 mM) or high extracellular K+ (130 mM), indicating that inflammasome activation in response to H/R might be mediated through K+ efflux and ROS production.
Conclusion: These findings demonstrate that initial activation of inflammasome in response to I/R occurs in CF, but not in CM, in the heart, and suggest that inflammasome in the CF could be a potential target for the treatment of myocardial I/R injury.