Abstract 197: Plasminogen Is Required for Hematopoietic Stem Cell-Mediated Cardiac Repair After Myocardial Infarction

Myocardial infarction (MI) is the primary cause of death throughout the United States. Granulocyte colony-stimulating factor (G-CSF) is used to mobilize hematopoietic progenitor and stem cells (HPSC) to improve cardiac recovery after MI. However, poor-mobilization to G-CSF is observed in 25% of patients and 10-20% of healthy donors. Therefore, a better understanding of the underlying mechanisms may offer novel approaches for G-CSF-mediated therapeutics. Our previous studies have identified an essential role of Plg in HPSC mobilization from bone marrow (BM) in response to G-CSF. Here, we investigate the role of Plg in G-CSF-stimulated cardiac repair after MI. Our data show that G-CSF significantly improves cardiac repair including increasing neovascularization in the infarct area, and improving ejection fraction and LV internal diameter determined by echocardiogram in WT mice. No improvement on heart function is observed in Plg -/- mice, indicating Plg is required for G-CSF-regulated cardiac repair after MI. To investigate whether Plg regulates HPSC recruitment to the ischemic area, BM transplantation with EGFP-expressing BM cells was performed to visualize BM-derived stem cells in infarcted tissue. Our data show that G-CSF dramatically increases recruitment of GFP + cKit + cells (by 12 fold) in WT mice but not in Plg -/- mice. In addition, BM stem cell-derived vessels and arteries are infrequent in Plg -/- mice suggesting that Plg enhances cardiac repair by promoting stem cell recruitment to the lesion. In further studies, we investigated the role of Plg in the regulation of SDF-1/CXCR-4 axis, a major regulator for HPSC recruitment. Our results show that G-CSF significantly increases CXCR-4 expression in the infarcted area in WT mice. While G-CSF-induced CXCR-4 expression is markedly decreased (80%) in Plg -/- mice, suggesting Plg may regulate CXCR-4 expression during HSPC recruitment to injured heart. Interestingly, Plg does not affect SDF-1 expression in response to G-CSF treatment. Taken together, our findings have identified a critical role of Plg in HSPC recruitment to the lesion site and subsequent tissue repair after MI. Thus, targeting Plg may offer a new therapeutic strategy to improve G-CSF-mediated cardiac repair after MI.