Abstract 1613: Toll-like Receptors Modulate Ischemic Preconditioning through a Toll-IL-1 Receptor Domain-Containing Adaptor Protein Dependent Pathway
Recent studies have implicated Toll-like receptor 2 (TLR2) and 4 (TLR4) in upregulating the expression of proinflammatory cytokines following ischemia-reperfusion injury. Given that TLRs are part of a phylogenetically conserved innate stress response system that protects the host against exogenous “danger signals,” we hypothesized that TLR2 and TLR4 might be involved in ischemic preconditioning (IPC) in the heart. Accordingly, we used a buffer perfused Langendorff apparatus to perform IPC in mice deficient in TLR2 (TLR2-D) and TLR4 (TLR4-D), as well as mice deficient in Toll-IL-1 Receptor Domain-Containing Adaptor Protein (TIRAP-D), a cytoplasmic adaptor protein that is critical for TLR2/4 signaling. Hearts were subjected to 30 min ischemia and 60 min reperfusion with or without 3 cycles of 2 min ischemia and 5 min reperfusion preconditioning.
Results: Following IPC the percent recovery of left ventricle (LV) developed pressure increased from 32.78±3.02% to 54.36±2.71% (p>0.05) in wild-type (WT) mice, whereas TIRAP-D mice showed no improvement in LV function following IPC (41.83±1.52% to 43.77±1.90%; P>0.05). Western blotting showed that the loss of IPC-induced cardioprotection in TIRAP-D mice was accompanied by decreased translocation of Protein Kinase C-epsilon (PKCϵ) to the membrane. In contrast to TIRAP-D mice, IPC resulted in a partial improvement in LV developed pressure in TLR2-D (33.22±1.27% to 41.75±3.18%; P<0.05) and TLR4-D mice (35.31±1.76% to 54.80±3.70%; p <0.05), suggesting that the presence of either TLR2 or TLR4, may partially compensate for the lack of the other receptor during IPC.
Conclusion: Our results suggest that IPC in the heart is mediated by TLR signaling through a TIRAP dependent pathway that leads to activation and translocation of PKCϵ.