Toll-like receptor 4 mediates ischemia/reperfusion injury of the heart.
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-kappaB 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-alpha, interleukin-1beta, 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 <.05). In both groups, nuclear factor-kappaB and activator protein-1 nuclear translocation occurred in the myocardium during myocardial ischemia/reperfusion injury, but, by densitometric analysis, nuclear translocation of nuclear factor-kappaB and activator protein-1 was significantly decreased in C3H/HeJ mice compared with C3H/HeN mice. Interleukin-1beta, monocyte chemotactic factor-1, and interleukin-6 were detectable in reperfused ischemic myocardium but were not detected in sham-operated myocardium; the expression of each of these mediators was significantly decreased in the myocardial tissue of C3H/HeJ mice when compared with expression in the control C3H/HeN mouse strain.


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.
Chong
Albert J
AJ
Division of Cardiothoracic Surgery, Department of Surgery, The University of Washington, 1959 NE Pacific Street, Seattle, WA 98195, USA.
Shimamoto
Akira
A
Hampton
Craig R
CR
Takayama
Hiroo
H
Spring
Denise J
DJ
Rothnie
Christine L
CL
Yada
Masaki
M
Pohlman
Timothy H
TH
Verrier
Edward D
ED
D000818:Animals; D018836:Inflammation Mediators / Q000502:physiology; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008809:Mice, Inbred C3H; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D009203:Myocardial Infarction / Q000209:etiology; D015428:Myocardial Reperfusion Injury / Q000209:etiology*; D011956:Receptors, Cell Surface / Q000502:physiology*; D051193:Toll-Like Receptors
D018836:Inflammation Mediators; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D051193:Toll-Like Receptors; D020928:Mitogen-Activated Protein Kinases