|
|
Toll-like Receptor 4 Mediates Myocardial Ischemic Preconditioning
M. L. Agnew1, D. J. Spring1, C. L. Rothnie1, A. J. Fleisig1, A. Shimamoto2, S. Shomura1, E. D. Verrier*1. 1University of Washington School of Medicine, Seattle, WA, 2Mie University Gradute School of Medicine, Tsu, Japan,
BACKGROUND: Previous work has demonstrated that the innate immune system, via toll-like receptor 4 (TLR4), contributes to myocardial ischemia-reperfusion (I/R) injury following prolonged ischemia. Our objective is to determine whether TLR4 also mediates the protective myocardial response to brief episodes of ischemia, known as ischemic preconditioning (IPC).
METHODS: Wild-type C57/BL6 mice (WT) were compared to TLR4- and MyD88-knockout mice (TLR4-/-, MyD88-/-) in three experimental groups. Group 1 underwent 30 minutes of regional myocardial ischemia followed by two hours of reperfusion (I/R alone). Group 2 underwent an IPC protocol prior to I/R. In Groups 1 and 2, infarct size was determined at the end of reperfusion. Group 3 underwent IPC only, after which hearts were harvested for molecular analysis via Western blot, electrophorectic mobility shift assay, and ribonuclease protection assay.
RESULTS: Compared to I/R alone, IPC decreased infarct size in WT (38.1% to 18.0%, p<.00001) but increased infarct size in TLR4-/- (22.6% to 36.9%, p<0.002); MyD88-/- was unchanged (25.1% to 22.7%). Compared to sham controls, IPC in WT led to significant phosphorylation of JNK and Akt, and increased nuclear translocation of NF-κB. Similar increases were not observed in TLR4-/-.
CONCLUSIONS: We provide evidence for a protective role of the innate immune system in myocardial preconditioning. These data indicate that IPC is mediated via TLR4 in a MyD88-independent fashion, leading to activation of the inflammatory kinase JNK and the survival kinase PI3K/Akt, nuclear translocation of NF-κB, and protection against infarct. This is the first experimental demonstration that TLR4 is involved in IPC.
Back to 32nd Annual Meeting
Back to Program Outline
|
