Abstract 1773: Cardiac Toll-Like Receptor 4 as a Determinant of Neutrophil Infiltration after Global Myocardial Ischemia/Reperfusion: Up-Regulation of Chemokine Expression in Response to Extracellular 70 kDa Heat Shock Cognate Protein
Cardiac surgery with global myocardial ischemia and reperfusion (I/R) causes an inflammatory response involving up-regulation of chemokine expression. Chemokines play a pivotal role in the inflammatory response by inducing leukocyte infiltration and activation. Although the mechanisms underlying myocardial chemokine expression after global myocardial I/R are unclear, several studies have suggested that Toll-like receptor 4 (TLR4) signaling can be activated by endogenous agents released from injured cells. And in a recent study we demonstrated, using an isolated mouse heart model, that the 70 kDa heat shock cognate protein (HSC70) is released from the myocardium after global myocardial I/R and induces expression of TNF-α, IL-1β and IL-6 via a TLR4-dependent mechanism. The purposes of this study were to determine, in the setting of global myocardial I/R:
the relative roles of cardiac and neutrophil TLR4 in myocardial neutrophil infiltration,
the effect of TLR4 signaling on myocardial chemokine expression and
the role of HSC70 in TLR4-mediated chemokine expression.
Methods and results: We subjected hearts isolated from C3H/HeJ (TLR4-defective, with non-functional TLR4) and C3H/HeN (TLR4-competent) mice to global myocardial I/R via the Langendorff technique. When we perfused them with TLR4-competent or TLR4-defective neutrophils during reperfusion, neutrophil infiltration in TLR4-defective hearts was significantly less than in TLR4-competent hearts, regardless of neutrophil phenotype. Myocardial expression of KC (the murine analogue of human IL-8) and MCP-1 after global myocardial I/R were markedly reduced in TLR4-defective hearts. Treatment with recombinant HSC70 increased chemokine expression in TLR4-competent but not TLR4-defective hearts, whereas treatment with an anti-HSC70 antibody reduced myocardial chemokine expression induced by I/R.
Conclusion: This study demonstrates that cardiac TLR4 and not neutrophil TLR4 plays a critical role in post-ischemic myocardial neutrophil infiltration in a murine model of global myocardial I/R. Myocardial TLR4 signaling regulates chemokine expression, and extracellular HSC70 is involved, at least in part, in TLR4-mediated myocardial chemokine expression.