Abstract 5285: In Vivo Real Time Monitoring of Stem Cells Homing in Postischemic Tissues
Hematopoietic stem cells (HSCs) are thought to repair postischemic tissues, but little is known about their homing to target tissues. Leukocytes migrate to postischemic tissues via the “three step” paradigm: rolling, adhesion, extravasation. HSCs express common surface markers with leukocytes and show enhanced migration in response to proinflammatory cytokines: HSCs might thus be taken up in postischemic tissues similarly to leukocytes. We thus evaluated whether HSC homing in postischemic tissues follows the three-step paradigm and it is influenced by degree of ischemia (I). Rat cremaster muscle was subjected to I of variable length (5, 30 or 180 min), followed by 90 min of reflow (R). At 45 min into R, 20 million fluorescent-labeled HSCs was infused IV, and their passage through microcirculation was evaluated by in vivo videomicroscopy for additional 45 min. At the end of experiment, adhering HSCs in cremaster muscle were counted, and recruitment in tissue evaluated by real time PCR of CD34 mRNA expression. In sham-operated rats (no ischemia), HSC-vessel wall interaction was very modest. In contrast, after I/R, HSCs showed rolling and adhesion behavior (left panels); HSC recruitment increased with increased length of I (right panel); by RT-PCR, muscles subjected to 180 min of I showed a median value of CD34 mRNA expression 9.9 times (range 2.3–20.6) greater than contralateral non-ischemic muscle. Thus, direct visualization of HSC in skeletal muscle shows that recruitment is low under normal conditions, while during postischemic reflow HSC recruitment through rolling/adhesion/extravasation is markedly increased, and appears to be enhanced by the severity of ischemic injury.