TLR3Deficency Protects The Myocardium From Ischemia/reperfusion Injury

Innate immune and inflammatory responses are involved in the pathophysiology of myocardial ischemia/reperfusion (I/R) injury. Toll-like receptors (TLRs) are important receptors in the recognition of pathogen-associated molecular patterns (PAMPs) and transduce a signal into the cell. There are at least11and13TLRs identified so far in humans and mice and they can recognize different ligands, For example, TLR1,2,4,5,6are involved in the recognition of structured unique to bacteria or fungi, while TLR3,7,8,9recognize viral or bacterial nucleic acids. TLRs involves five adaptor proteins known as MyD88(myeloid differentiation primary response protein)、Mal (MyD88adaptor-like protein)、TRIF (TIR-domain-containing adaptor protein inducing IFNβ-mediated transcription-factor)、TRAM (TRIF-related adaptor molecule)、SARM(sterile alpha and HEAT-Armadillo motifs). When bound by ligands, TLRs active two signaling pathways:MyD88dependent pathway and MyD88independent pathway. It is reported that TLR4and TLR2plays an important role in several important cardiac diseases including I/R injury. TLR3is located in intracellular endosomes and recognizes double stranded RNA, resulting in induction of antiviral immune responses. TLR3also recognized by products from apoptotic and necrotic cells. By binding its ligands, TLR3activates transcriptional factor NF-κB and interferon regulatory factor3(IRF3) via MyD88independent but TRIF dependent pathway, leading to the production of pro-inflammatory factors and type1interferon. More significantly, recent studies demonstrated that TLR3has an major role in hyperoxia-induced aute lung injury and infalmmation. In addition, the activation of TLR3in tummor cells leads to the cell apoptosis. However, the role of TLR3in myocardial I/R injury has not been investigated entirely.This study examined the role of TLR3in myocardial in ischemic and reperfusion injury. TLR3knockout (TLR3-/-,n=8mice/group), that were crossbreed with wild type, and age-matched wild type(WT,n=8mice/group) mice were subjected to myocardial ischemia (45min) followed by reperfusion. Cardiac function was measured by echocardiography before and24h,3d,7d,14d after I/R.Hearts were harvested4h after I/R and cellular proteins were isolated for immunoblots. Results:TLR3deficency mice significantly decreased IA/RA by42.16%(39.38±2.19%vs68.09±2.04%, n=8mice/group, P<0.05), and IA/LV by45.48%(23.84±1.03%vs43.73±1.09%, n=8mice/group, P<0.05), compared with WT I/R group. Ejection fraction and fractional shortening in TLR3deficient mice were also significantly increased respectively compared with WT I/R group. I/R resulted in significant apoptosis as evidenced by Tunnel assay. However, TLR3deficency significantly decreased I/R-induced cardic myocyte apoptosis and also attenuated I/R-induced FAS, FASL, FADD, BAX, BAK expression in the myocardium. I/R activation of NF-κB binding activity was prevent by TLR3deficiency. In addition, TLR3deficient mice reduced levels of IL-1β by51.43%(17.3±2.39vs35.4±1.96pg/ml, P<0.05), and TNF-α by35.56%(0.50±0.09vs0.90±0.046pg/ml, P<0.05) in the plasma compared with the WT I/R group. Also, I/R-increased VCAM and ICAM expression in the myocardial vascular were attenuated in TLR3deficient mice. More significantly, the number of macrophage in the myocardium in TLR3deficient mice were decreased compared with the WT I/R group. In addition, TLR3-/-can inhibit the infiltration of neutrophil compared with the WT I/R group. Conclusions:The results indicated that TLR3plays a deleterious role in mediating cardiac dysfunction in myocardial I/R injury. Thus, modulation of TLR3activity may be a strategy for reducing myocardial ischemic injury.