Abstract 5411: Hmgb1 in Ischemia-Reperfusion Injury of the Heart
High-mobility group box-1 (HMGB1) is a nuclear factor released by necrotic cells and by activated immune cells. HMGB1 signals via members of the toll-like receptor (TLR) family and the receptor for advanced glycation end products (RAGE). Although HMGB1 has been implicated in ischemia reperfusion (I/R) injury of the liver and lung, its role in I/R injury of the heart remains unclear. Here we demonstrate that HMGB1 acts as an early mediator of inflammation and organ damage in I/R injury of the heart. HMGB1 levels were already elevated 30 minutes after hypoxia in vitro and in ischemic injury of the heart in vivo on both RNA and protein level. Treatment of mice with recombinant (r)HMGB1 resulted in increased infarction sizes (81.1±8.4% vs. 60.5±8.2%, n=10, p<0.005) and reduced fractional shortening (25±0.6% vs. 29±1.1%, n=10, p<0.05) and increased sTroponin T (TnT) release (9.7±1.4μg/l vs. 7.6 ± 1.4μg/l, n=10, p<0.005). In contrast, both HMGB1 box A treated WT- and RAGE−/− mice demonstrated significantly reduced infarction sizes (21.9±8.1% vs. 60.5±8.2%, n=10, p<0.005; and 35.0±6.5% vs. 60.5±8.2%, n=10, p<0.0001) and improved recovery of cardiac function (42.0±1.1% vs. 29.0±1.1%, n=10, p<0.01 and 37.0±1.2% vs. 29.0±1.1%, n=10, p<0.01) compared to untreated WT-mice undergoing I/R. In addition, HMGB1 inhibition with rHMGB1 box A suggested an involvement of the MAP kinases JNK and ERK1/2 as well as the nuclear transcription factor NF-κB in I/R injury. Interestingly, infarct size and markers of tissue damage were not affected by administration of rHMGB1 or HMGB1-antagonists in RAGE−/− mice which demonstrated significantly reduced damage in reperfused hearts compared to wildtype (WT) mice. Coincubation studies using rHMGB1 in vitro induced an inflammatory response in isolated macrophages from WT mice, but not in macrophages from RAGE−/− mice. HMGB1 plays a major role in the early event of I/R injury by binding to RAGE resulting in the activation of proinflammatory pathways and enhanced myocardial injury. Therefore, blockage of HMGB1 might represent a novel therapeutic strategy in I/R injury.