Abstract 350: Toll-like Receptor 2 Activation, Especially In Circulating Leukocytes, Mediates Myocardial Ischemia/Reperfusion Injury In Mice

Abstract

OBJECTIVES. Myocardial ischemia/reperfusion (MI/R) injury is characterized by an inflammatory response through NF-κB, increase of infarct size and worsening of cardiac function. Toll-like receptors (TLRs) are part of innate immunity and initiate the same inflammatory reaction. Here we studied in vivo to what extent TLR2 is involved in myocardial damage and what the relative contribution is of TLR2 expression in parenchymal cells and leukocytes to myocardial damage during MI/R in mice. METHODS. C57Bl6J mice underwent 30 minutes ischemia - 24 hours of reperfusion. Four experimental groups were studied: TLR2 knock-out (TLR2 KO) mice (n=10), saline treated wild-type (WT) mice (n=10), generated chimeric WT mice with TLR2 KO bone marrow (BLOOD KO; n=7) and chimeric TLR2 KO mice with WT hematopoietic cells (ORGAN KO; n=7). Saline was administered via the tail vein 5 minutes prior to reperfusion. After 24 hours, the LCA was ligated again at the level marked by the suture left in place. Mice were terminated and infarct size (IS) was measured as a percentage of the area at risk (AAR) using 4% Evans’ blue dye injection in the aortic root and triphenyltetrazolium chloride (TTC) staining (fig. 1). Data are presented as Mean±SEM. RESULTS. The AAR as percentage of the left ventricle was similar between groups: TLR2 KO 41%, saline 41%, Blood KO 41%, Organ KO 42%. Saline treatment resulted in 34.5%±3.3 of infarction, whereas in TLR2 KO mice infarct size decreased to 23.0%±2.9 (p=0.029 vs. saline). Infarct size in BLOOD KO mice was 22.9%±2.7 (p=0.024 vs. saline), while ORGAN KO mice had 33.9%±3.2 (p=0.998 vs. saline) of infarction within the area at risk (fig. 2). CONCLUSION. TLR2 deficiency significantly reduces infarct size with ~33% compared to saline treatment in mice after 30 minutes of ischemia and 24 hours of reperfusion. We show for the first time that TLR2 expression in circulating leukocytes plays an important role in infarction after MI/R injury. Systemic inhibition of TLR2 may be a potential therapeutic target in the treatment of patients with acute myocardial infarction.