Abstract 12135: Toll-like Receptor Signalling Mediates C-kit+ Cell Migration in vivo Following Ischemia-reperfusion Injury via the Myd88 Pathway

Introduction: Toll-like-receptor (TLR) mediated signalling has been shown to regulate tissue damage following cardiac ischemia-reperfusion (I-R) injury. Whether progenitor cell based cardiac regeneration might also depend on TLR-signaling has not been described conclusively. As sufficient progenitor cell migration represents a crucial step of cell-based therapy protocols, we aimed at analyzing the migratory capacity of c-kit+ bone marrow stem cells in vivo following I-R injury as well as the impact of endothelial TLR's and related signalling pathways (MyD88,TRIF)on c-kit+ cell migration. Methods: Murine c-kit+ stem cells were isolated from the bone marrow. In vivo migration of fluorescently labeled c-kit+ following different extents of local I-R injury was visualized by intravital fluorescence microscopy, utilizing the cremaster muscle model in male mice.C-kit+ cell migration was quantified by analyzing early (endothelial rolling) and late (firm endothelial adhesion) c-kit+ cell interaction with the local endothelium. The role of TLR-2 and TLR-4, as well as MyD88 and TRIF on c-kit+ migration following I-R-injury was analyzed by applying specific knock-out models. Results: A sequence of 15 min ischemia followed by 15 min reperfusion induced relevant interactions of c-kit+ cells with the microvascular endothelium(Firm endothelial adhesion:5.6±1.3 cells/mm2 in control vs. 30.2±10.1 cells/mm2 in IR, p<0.05). Prolonged I-R periods did not result in an additional gain of c-kit+ cell-endothelial cell interaction. Knock-out of TLR-2 and TLR-4 diminished I-R induced c-kit+ - endothelial cell interaction.Subsequent knock-out of downstream adaptor proteins resulted in a significantly decreased firm endothelial c-kit+ cell adhesion only for MyD88 but not for TRIF. Conclusions: Artificially applied c-kit+ cells are capable to interact with the target organ endothelium following I-R injury. C-kit+ cell-endothelial cell interaction following I-R injury depends on TLR associated signaling, with a special relevance being demonstrated here for the MyD88 pathway. Our findings suggest, that therapeutic blockade of TLR signaling following I-R injury for anti-inflammatory purposes might interfere with progenitor cell based therapy protocols.