Abstract 13: Plasminogen Is Required for Hematopoietic Stem Cell-Mediated Cardiac Repair After Myocardial Infarction

Ischemic heart disease, including myocardial infarction (MI), is the primary cause of death throughout the US. 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 regulating G-CSF-induced cardiac repair may offer novel approaches for strengthening stem cell-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 tissue repair including increasing neovascularization in the infarct area, and improving ejection fraction and LV internal diameter by echocardiogram in wild-type mice. No improvement in tissue repair and heart function by G-CSF is observed in Plg -/- mice, indicating that Plg is required for G-CSF-regulated cardiac repair after MI. To investigate whether Plg regulates HPSC recruitment to ischemia area, bone marrow transplantion (BMT) 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+ cells (by 16 fold) in WT mice but not in Plg -/- mice, suggesting that Plg is essential for HPSC recruitment from BM to the lesion sites after MI. 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 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.