Toll-like receptors 2-deficient mice are protected against postischemic coronary endothelial dysfunction

Objectives - Toll-like receptors (TLR) 2 are expressed in cardiac and inflammatory cells, and regulate leukocyte function. Because leukocyte adhesion is a critical event in endothelial injury induced by ischemia/reperfusion (I/R), we assessed whether TLR2 were involved in I/R - induced coronary endothelial injury. Methods and Results - Ischemia-reperfusion markedly decreased NO-mediated coronary relaxations to acetylcholine assessed ex vivo. In contrast, in TLR2 deficient mice, I/R paradoxically improved the NO-mediated responses to acetylcholine. To precise the cellular compartment expressing TLR2 which is involved in endothelial injury, we developed bone-marrow chimeric mice by transplanting TLR2(-/-) bone marrow to WT mice or WT bone marrow to TLR2(-/-) mice and submitted them to I/R 5 weeks after transplant. Both chimeric mice displayed similar protection as TLR2(-/-) mice against I/R-induced endothelial dysfunction, suggesting a role of TLR2 expressed on both non-bone marrow cells (in our case presumably endothelial cells and/or cardiomyocytes) and cells of bone marrow origin (presumably neutrophils). TLR2 deficiency was also associated with a smaller infarct size, and reduced reperfusion-induced production of reactive oxygen species and leukocyte infiltration. Conclusions - TLR2 contribute to coronary endothelial dysfunction after I/R, possibly through stimulation of neutrophil- (and free radical-) mediated endothelial injury.