Abstract 1141: Modulation of Toll-Like Receptor 4 mediated NFκB Activation Signaling Pathway Protects the Myocardium from Ischemia/Reperfusion Injury
Recent evidence suggests that innate immunity is involved in myocardial ischemia/reperfusion (I/R) injury. However, the mechanisms by which the innate immune pathways participate in myocardial ischemic injury have not been elucidated. Toll-like receptors (TLRs) play a critical role in the induction of innate and adaptive immunity. We have shown that I/R significantly increased myocardial NFκB activation and that modulation of TLR4 mediated signaling by glucan rapidly induces cardioprotection, suggesting that TLR4 mediated signaling pathway plays a role in myocardial ischemic injury. In the present study, we examined effects of blockade of TLR4 mediated NFκB pathway on the myocardial infarction. Rat hearts were transfected with Ad5-IκBα mutant (1× 1010 pfu/ml, plaque forming units) to inhibit NFκB activation or Ad5-dominate negative MyD88 (Ad5-dnMyD88, 1× 1010 pfu/ml) to block MyD88-mediated pathway. Ad5-GFP served as control. Three days after transfection, the hearts were subjected to ischemia for 45 min followed by reperfusion for 4 hrs. To investigate the role of TLR4 in myocardial ischemic injury, TLR4 knockout mice were subjected to ischemia (45 min) and reperfusion (4 hrs). Wild type (WT) mice served as control. The myocardial infarction was determined by TTC staining. Transfection of Ad5-IκBα mutant significantly reduced myocardial infarct size [13.69 ± 7.02% (IκBα mutant, n=4) vs 34.25 ± 4.09% (control, n=4)], while Ad5-GFP did not [32.27± 11.56% (GFP, n=4) vs 34.25 ± 4.09% (control, n=4)]. Transfection of Ad5-dnMyD88 significantly reduced infarct size by 53.6% compared with I/R group [15.1 ± 3.02% (n=8) vs 32.5 ± 2.59% (n=8)] but transfection of Ad5-GFP did not [35.4 ± 2.59% (n=8) vs 32.5 ± 2.59% (n=8)]. I/R significantly induced infarct size/area at risk by 40.6 ± 2.78% in WT mice (n=8) and by 19.2 ± 2.79% in TLR4 knockout mice (n=8). Blockade of PI3K/Akt signaling pathway by LY294002 or Wortmannin abrogated the myocardial protection from I/R injury in TLR4 knockout mice. Our results suggest that TLR4 mediated MyD88-dependent NFκB activation pathway could be targets for protection of myocardium from ischemic injury and that the PI3K/Akt signaling pathway contributes to the cardioprotection of TLR4 knockout mice following I/R induced injury.