Toll-like receptor 4 mediates ischemia/reperfusion injury of the heart

Abstract Background Restoration of blood flow to the ischemic heart may paradoxically exacerbate tissue injury (ischemia/reperfusion injury). Toll-like receptor 4, expressed on several cell types, including cardiomyocytes, is a mediator of the host inflammatory response to infection. Because ischemia/reperfusion injury is characterized by an acute inflammatory reaction, we investigated toll-like receptor 4 activation in a murine model of regional myocardial ischemia/reperfusion injury. We used C3H/HeJ mice, which express a nonfunctional toll-like receptor 4, to assess the pertinence of this receptor to tissue injury after reperfusion of ischemic myocardium. Methods Wild-type mice (C3H/HeN) or toll-like receptor 4 mutant mice (C3H/HeJ) were subjected to 60 minutes of regional myocardial ischemia followed by 2 hours of reperfusion. At the end of reperfusion, the area at risk and the myocardial infarct size were measured as the end point of myocardial ischemia/reperfusion injury. Myocardial mitogen-activated protein kinase activation was measured by Western blotting, and nuclear translocation of nuclear factor-κB and activator protein-1 was determined by electrophoretic mobility shift assay. Ischemia/reperfusion–injured myocardium was also assessed by ribonuclease protection assay for expression of inflammatory mediators (tumor necrosis factor-α, interleukin-1β, monocyte chemotactic factor-1, and interleukin-6). Results The area at risk was similar for all groups after myocardial ischemia/reperfusion injury. There was a 40% reduction in infarct size (as a percentage of the area at risk) in C3H/HeJ mice compared with C3H/HeN mice ( P = .001). Within the myocardium, significant activation of c-Jun N-terminal kinase, p38, and extracellular signal-regulated kinase was observed in both strains after ischemia and during reperfusion as compared with an absence of mitogen-activated protein kinase activation during sham operations; however, c-Jun N-terminal kinase activity, but not p38 or extracellular signal-regulated kinase activity, was significantly reduced in C3H/HeJ mice ( P Conclusions Our data suggest that toll-like receptor 4 may mediate, at least in part, myocardial ischemia/reperfusion injury. Inhibition of toll-like receptor 4 activation may be a potential therapeutic target to attenuate ischemia/reperfusion-induced tissue damage in the clinical setting.