Ablation of Toll-like receptor 9 attenuates myocardial ischemia/reperfusion injury in mice

In myocardial ischemia/reperfusion injury, the innate immune and subsequent inflammatory responses play a crucial role in the extension of myocardial damage. Toll-like receptor 9 (TLR9) is a critical receptor for recognizing unmethylated CpG motifs that mitochondria contain in their DNA, and induces inflammatory responses. The aim of this study was to elucidate the role of TLR9 in myocardial ischemia/reperfusion injury. Isolated hearts from TLR9-deficient and control wild-type mice were subjected to 35 min of global ischemia, followed by 60 min of reperfusion with Langendorff apparatus. Furthermore, wild-type mouse hearts were infused with DNase I and subjected to ischemia/reperfusion. Ablation of TLR9-mediated signaling pathway attenuates myocardial ischemia/reperfusion injury and inflammatory responses, and digestion of extracellular mitochondrial DNA released from the infarct heart partially improved myocardial ischemia/reperfusion injury with no effect on inflammatory responses. TLR9 could be a therapeutic target to reduce myocardial ischemia/reperfusion injury.