Hematopoietic stem cells (HSCs) have been shown to migrate to injury sites and aid in tissue repair. However, while benefits are observed in experimental studies, clinical success is poor and may partially be due to limited HSC recruitment. We hypothesised that HSC pre-treatment with hydrogen peroxide (H2O2), known to be released within ischemic sites, would enhance their recruitment to injured gut.Methods
HSCs were pre-treated with 100μM H2O2 or PBS for one hour. Anaesthetised (ketamine/xylazine) mice were subjected to intestinal ischemia-reperfusion (IR) injury and HSC recruitment in the small intestine was examined intravitally. HSC adhesion to endothelial cells and frozen IR injured gut sections was also quantitated in vitro. HSC integrin expression, clustering and avidity were also examined following H2O2 treatment. In addition, HSCs were analysed for viability following treatment to ensure the absence of cell death.Results
Treating HSCs with H2O2 significantly enhanced adhesion to both murine colonic endothelial cells and injured gut sections when compared to PBS treated HSCs. Importantly, treating HSCs with 100μM H2O2 significantly enhanced their adhesion in the IR injured murine gut microvasculature. A concomitant reduction in pulmonary HSC adhesion was also observed in vivo following cell treatment with H2O2. Treatment of HSCs with H2O2 significantly enhanced their recruitment on ICAM-1/VCAM-1 coated surfaces; this adhesion was dependent on CD18 and CD49d respectively. While H2O2 treatment did not enhance surface CD18 or CD49d expression, H2O2 treatment did promote integrin clustering on the HSC surface. Furthermore, FITC-phalloidin staining of F-actin was significantly enhanced following treatment with H2O2 compared to PBS treated controls. Importantly, 100μM H2O2 treatment did not cause cell death when compared to PBS treated control cells. H2O2 treated HSCs are still capable of haematopoietic differentiation, confirming their functional viability following treatment.Conclusion
HSC recruitment to injured gut can be modulated by H2O2. Importantly, this study highlights that maximal HSC recruitment within ischemic organs is not achieved by injury alone. H2O2 may enhance homing through increased avidity of integrins or by stimulating the cellular migratory apparatus, thus rendering HSCs more likely to migrate towards chemotactic stimuli. Strategies that enhance HSC recruitment may improve their therapeutic efficacy.